\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename gfortran.info
-@set copyrights-gfortran 1999-2008
+@set copyrights-gfortran 1999-2021
@include gcc-common.texi
Copyright @copyright{} @value{copyrights-gfortran} Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
-under the terms of the GNU Free Documentation License, Version 1.2 or
+under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being ``Funding Free Software'', the Front-Cover
Texts being (a) (see below), and with the Back-Cover Texts being (b)
@top Introduction
@cindex Introduction
-This manual documents the use of @command{gfortran},
-the GNU Fortran compiler. You can find in this manual how to invoke
+This manual documents the use of @command{gfortran},
+the GNU Fortran compiler. You can find in this manual how to invoke
@command{gfortran}, as well as its features and incompatibilities.
@ifset DEVELOPMENT
* Runtime:: Influencing runtime behavior with environment variables.
Part II: Language Reference
-* Fortran 2003 and 2008 status:: Fortran 2003 and 2008 features supported by GNU Fortran.
-* Extensions:: Language extensions implemented by GNU Fortran.
+* Fortran standards status:: Fortran 2003, 2008 and 2018 features supported by GNU Fortran.
+* Compiler Characteristics:: User-visible implementation details.
+* Extensions:: Language extensions implemented by GNU Fortran.
+* Mixed-Language Programming:: Interoperability with C
+* Coarray Programming::
* Intrinsic Procedures:: Intrinsic procedures supported by GNU Fortran.
* Intrinsic Modules:: Intrinsic modules supported by GNU Fortran.
@c The following duplicates the text on the TexInfo table of contents.
@iftex
This manual documents the use of @command{gfortran}, the GNU Fortran
-compiler. You can find in this manual how to invoke @command{gfortran},
+compiler. You can find in this manual how to invoke @command{gfortran},
as well as its features and incompatibilities.
@ifset DEVELOPMENT
The GNU Fortran compiler front end was
designed initially as a free replacement for,
-or alternative to, the unix @command{f95} command;
-@command{gfortran} is the command you'll use to invoke the compiler.
+or alternative to, the Unix @command{f95} command;
+@command{gfortran} is the command you will use to invoke the compiler.
@menu
* About GNU Fortran:: What you should know about the GNU Fortran compiler.
@node About GNU Fortran
@section About GNU Fortran
-The GNU Fortran compiler is still in an early state of development.
-It can generate code for most constructs and expressions,
-but much work remains to be done.
-
-When the GNU Fortran compiler is finished,
-it will do everything you expect from any decent compiler:
+The GNU Fortran compiler supports the Fortran 77, 90 and 95 standards
+completely, parts of the Fortran 2003, 2008 and 2018 standards, and
+several vendor extensions. The development goal is to provide the
+following features:
@itemize @bullet
@item
-Read a user's program,
-stored in a file and containing instructions written
-in Fortran 77, Fortran 90, Fortran 95, Fortran 2003 or Fortran 2008.
-This file contains @dfn{source code}.
+Read a user's program, stored in a file and containing instructions
+written in Fortran 77, Fortran 90, Fortran 95, Fortran 2003, Fortran
+2008 or Fortran 2018. This file contains @dfn{source code}.
@item
Translate the user's program into instructions a computer
@dfn{machine code},
code designed to be efficiently translated and processed
by a machine such as your computer.
-Humans usually aren't as good writing machine code
+Humans usually are not as good writing machine code
as they are at writing Fortran (or C++, Ada, or Java),
because it is easy to make tiny mistakes writing machine code.
@item
Provide information in the generated machine code that can
make it easier to find bugs in the program (using a debugging tool,
-called a @dfn{debugger}, such as the GNU Debugger @command{gdb}).
+called a @dfn{debugger}, such as the GNU Debugger @command{gdb}).
@item
Locate and gather machine code already generated to
perform actions requested by statements in the user's program.
This machine code is organized into @dfn{modules} and is located
-and @dfn{linked} to the user program.
+and @dfn{linked} to the user program.
@end itemize
The GNU Fortran compiler consists of several components:
which provides the command-line interface for the compiler. It calls
the relevant compiler front-end program (e.g., @command{f951} for
Fortran) for each file in the source code, and then calls the assembler
-and linker as appropriate to produce the compiled output. In a copy of
+and linker as appropriate to produce the compiled output. In a copy of
GCC which has been compiled with Fortran language support enabled,
@command{gcc} will recognize files with @file{.f}, @file{.for}, @file{.ftn},
@file{.f90}, @file{.f95}, @file{.f03} and @file{.f08} extensions as
-Fortran source code, and compile it accordingly. A @command{gfortran}
+Fortran source code, and compile it accordingly. A @command{gfortran}
driver program is also provided, which is identical to @command{gcc}
except that it automatically links the Fortran runtime libraries into the
compiled program.
Source files with @file{.f90}, @file{.f95}, @file{.f03}, @file{.f08},
@file{.F90}, @file{.F95}, @file{.F03} and @file{.F08} extensions are
treated as free form. The capitalized versions of either form are run
-through preprocessing. Source files with the lower case @file{.fpp}
+through preprocessing. Source files with the lower case @file{.fpp}
extension are also run through preprocessing.
This manual specifically documents the Fortran front end, which handles
the programming language's syntax and semantics. The aspects of GCC
which relate to the optimization passes and the back-end code generation
-are documented in the GCC manual; see
+are documented in the GCC manual; see
@ref{Top,,Introduction,gcc,Using the GNU Compiler Collection (GCC)}.
The two manuals together provide a complete reference for the GNU
Fortran compiler.
Many Fortran compilers including GNU Fortran allow passing the source code
through a C preprocessor (CPP; sometimes also called the Fortran preprocessor,
-FPP) to allow for conditional compilation. In the case of GNU Fortran,
-this is the GNU C Preprocessor in the traditional mode. On systems with
+FPP) to allow for conditional compilation. In the case of GNU Fortran,
+this is the GNU C Preprocessor in the traditional mode. On systems with
case-preserving file names, the preprocessor is automatically invoked if the
-filename extension is @code{.F}, @code{.FOR}, @code{.FTN}, @code{.fpp},
-@code{.FPP}, @code{.F90}, @code{.F95}, @code{.F03} or @code{.F08}. To manually
+filename extension is @file{.F}, @file{.FOR}, @file{.FTN}, @file{.fpp},
+@file{.FPP}, @file{.F90}, @file{.F95}, @file{.F03} or @file{.F08}. To manually
invoke the preprocessor on any file, use @option{-cpp}, to disable
preprocessing on files where the preprocessor is run automatically, use
@option{-nocpp}.
If a preprocessed file includes another file with the Fortran @code{INCLUDE}
-statement, the included file is not preprocessed. To preprocess included
+statement, the included file is not preprocessed. To preprocess included
files, use the equivalent preprocessor statement @code{#include}.
If GNU Fortran invokes the preprocessor, @code{__GFORTRAN__}
-is defined and @code{__GNUC__}, @code{__GNUC_MINOR__} and
+is defined. The macros @code{__GNUC__}, @code{__GNUC_MINOR__} and
@code{__GNUC_PATCHLEVEL__} can be used to determine the version of the
-compiler. See @ref{Top,,Overview,cpp,The C Preprocessor} for details.
+compiler. See @ref{Top,,Overview,cpp,The C Preprocessor} for details.
+
+GNU Fortran supports a number of @code{INTEGER} and @code{REAL} kind types
+in additional to the kind types required by the Fortran standard.
+The availability of any given kind type is architecture dependent. The
+following pre-defined preprocessor macros can be used to conditionally
+include code for these additional kind types: @code{__GFC_INT_1__},
+@code{__GFC_INT_2__}, @code{__GFC_INT_8__}, @code{__GFC_INT_16__},
+@code{__GFC_REAL_10__}, and @code{__GFC_REAL_16__}.
While CPP is the de-facto standard for preprocessing Fortran code,
Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines
Conditional Compilation, which is not widely used and not directly
-supported by the GNU Fortran compiler. You can use the program coco
-to preprocess such files (@uref{http://users.erols.com/dnagle/coco.html}).
+supported by the GNU Fortran compiler. You can use the program coco
+to preprocess such files (@uref{http://www.daniellnagle.com/coco.html}).
@c ---------------------------------------------------------------------
@cindex Fortran 77
@cindex @command{g77}
-The GNU Fortran compiler is the successor to @command{g77}, the Fortran
-77 front end included in GCC prior to version 4. It is an entirely new
-program that has been designed to provide Fortran 95 support and
-extensibility for future Fortran language standards, as well as providing
-backwards compatibility for Fortran 77 and nearly all of the GNU language
+The GNU Fortran compiler is the successor to @command{g77}, the Fortran
+77 front end included in GCC prior to version 4. It is an entirely new
+program that has been designed to provide Fortran 95 support and
+extensibility for future Fortran language standards, as well as providing
+backwards compatibility for Fortran 77 and nearly all of the GNU language
extensions supported by @command{g77}.
standard-compliant Fortran 95, Fortran 90, and Fortran 77 programs,
including a number of standard and non-standard extensions, and can be
used on real-world programs. In particular, the supported extensions
-include OpenMP, Cray-style pointers, and several Fortran 2003 and Fortran
-2008 features such as enumeration, stream I/O, and some of the
-enhancements to allocatable array support from TR 15581. However, it is
+include OpenMP, Cray-style pointers, some old vendor extensions, and several
+Fortran 2003 and Fortran 2008 features, including TR 15581. However, it is
still under development and has a few remaining rough edges.
+There also is initial support for OpenACC.
At present, the GNU Fortran compiler passes the
-@uref{http://www.fortran-2000.com/ArnaudRecipes/fcvs21_f95.html,
+@uref{http://www.fortran-2000.com/ArnaudRecipes/fcvs21_f95.html,
NIST Fortran 77 Test Suite}, and produces acceptable results on the
@uref{http://www.netlib.org/lapack/faq.html#1.21, LAPACK Test Suite}.
-It also provides respectable performance on
-the @uref{http://www.polyhedron.com/pb05.html, Polyhedron Fortran
+It also provides respectable performance on
+the @uref{http://www.polyhedron.com/fortran-compiler-comparisons/polyhedron-benchmark-suite,
+Polyhedron Fortran
compiler benchmarks} and the
-@uref{http://www.llnl.gov/asci_benchmarks/asci/limited/lfk/README.html,
+@uref{http://www.netlib.org/benchmark/livermore,
Livermore Fortran Kernels test}. It has been used to compile a number of
large real-world programs, including
-@uref{http://mysite.verizon.net/serveall/moene.pdf, the HIRLAM
-weather-forecasting code} and
-@uref{http://www.theochem.uwa.edu.au/tonto/, the Tonto quantum
-chemistry package}; see @url{http://gcc.gnu.org/wiki/GfortranApps} for an
-extended list.
+@uref{http://hirlam.org/, the HARMONIE and HIRLAM weather forecasting code} and
+@uref{http://physical-chemistry.scb.uwa.edu.au/tonto/wiki/index.php/Main_Page,
+the Tonto quantum chemistry package}; see
+@url{https://gcc.gnu.org/@/wiki/@/GfortranApps} for an extended list.
Among other things, the GNU Fortran compiler is intended as a replacement
for G77. At this point, nearly all programs that could be compiled with
regressions.
The primary work remaining to be done on GNU Fortran falls into three
-categories: bug fixing (primarily regarding the treatment of invalid code
-and providing useful error messages), improving the compiler optimizations
-and the performance of compiled code, and extending the compiler to support
-future standards---in particular, Fortran 2003.
+categories: bug fixing (primarily regarding the treatment of invalid
+code and providing useful error messages), improving the compiler
+optimizations and the performance of compiled code, and extending the
+compiler to support future standards---in particular, Fortran 2003,
+Fortran 2008 and Fortran 2018.
@c ---------------------------------------------------------------------
@section Standards
@cindex Standards
+@menu
+* Varying Length Character Strings::
+@end menu
+
The GNU Fortran compiler implements
ISO/IEC 1539:1997 (Fortran 95). As such, it can also compile essentially all
standard-compliant Fortran 90 and Fortran 77 programs. It also supports
-the ISO/IEC TR-15581 enhancements to allocatable arrays, and
-the @uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,
-OpenMP Application Program Interface v2.5} specification.
-
-In the future, the GNU Fortran compiler will also support ISO/IEC
-1539-1:2004 (Fortran 2003) and future Fortran standards. Partial support
-of that standard is already provided; the current status of Fortran 2003
-support is reported in the @ref{Fortran 2003 status} section of the
-documentation.
-
-The next version of the Fortran standard after Fortran 2003 is currently
-being developed and the GNU Fortran compiler supports some of its new
-features. This support is based on the latest draft of the standard
-(available from @url{http://www.nag.co.uk/sc22wg5/}) and no guarantee of
-future compatibility is made, as the final standard might differ from the
-draft. For more information, see the @ref{Fortran 2008 status} section.
+the ISO/IEC TR-15581 enhancements to allocatable arrays.
+
+GNU Fortran also have a partial support for ISO/IEC 1539-1:2004
+(Fortran 2003), ISO/IEC 1539-1:2010 (Fortran 2008), the Technical
+Specification @code{Further Interoperability of Fortran with C}
+(ISO/IEC TS 29113:2012). Full support of those standards and future
+Fortran standards is planned. The current status of the support is
+can be found in the @ref{Fortran 2003 status}, @ref{Fortran 2008
+status} and @ref{Fortran 2018 status} sections of the documentation.
+
+Additionally, the GNU Fortran compilers supports the OpenMP specification
+(version 4.5 and partial support of the features of the 5.0 version,
+@url{http://openmp.org/@/openmp-specifications/}).
+There also is support for the OpenACC specification (targeting
+version 2.6, @uref{http://www.openacc.org/}). See
+@uref{https://gcc.gnu.org/wiki/OpenACC} for more information.
+
+@node Varying Length Character Strings
+@subsection Varying Length Character Strings
+@cindex Varying length character strings
+@cindex Varying length strings
+@cindex strings, varying length
+
+The Fortran 95 standard specifies in Part 2 (ISO/IEC 1539-2:2000)
+varying length character strings. While GNU Fortran currently does not
+support such strings directly, there exist two Fortran implementations
+for them, which work with GNU Fortran. They can be found at
+@uref{http://www.fortran.com/@/iso_varying_string.f95} and at
+@uref{ftp://ftp.nag.co.uk/@/sc22wg5/@/ISO_VARYING_STRING/}.
+
+Deferred-length character strings of Fortran 2003 supports part of
+the features of @code{ISO_VARYING_STRING} and should be considered as
+replacement. (Namely, allocatable or pointers of the type
+@code{character(len=:)}.)
@c =====================================================================
Malformed environment variables are silently ignored.
@menu
+* TMPDIR:: Directory for scratch files
* GFORTRAN_STDIN_UNIT:: Unit number for standard input
* GFORTRAN_STDOUT_UNIT:: Unit number for standard output
* GFORTRAN_STDERR_UNIT:: Unit number for standard error
-* GFORTRAN_USE_STDERR:: Send library output to standard error
-* GFORTRAN_TMPDIR:: Directory for scratch files
-* GFORTRAN_UNBUFFERED_ALL:: Don't buffer I/O for all units.
-* GFORTRAN_UNBUFFERED_PRECONNECTED:: Don't buffer I/O for preconnected units.
+* GFORTRAN_UNBUFFERED_ALL:: Do not buffer I/O for all units
+* GFORTRAN_UNBUFFERED_PRECONNECTED:: Do not buffer I/O for preconnected units.
* GFORTRAN_SHOW_LOCUS:: Show location for runtime errors
* GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted
-* GFORTRAN_DEFAULT_RECL:: Default record length for new files
* GFORTRAN_LIST_SEPARATOR:: Separator for list output
* GFORTRAN_CONVERT_UNIT:: Set endianness for unformatted I/O
-* GFORTRAN_ERROR_DUMPCORE:: Dump core on run-time errors
* GFORTRAN_ERROR_BACKTRACE:: Show backtrace on run-time errors
+* GFORTRAN_FORMATTED_BUFFER_SIZE:: Buffer size for formatted files
+* GFORTRAN_UNFORMATTED_BUFFER_SIZE:: Buffer size for unformatted files
@end menu
+@node TMPDIR
+@section @env{TMPDIR}---Directory for scratch files
+
+When opening a file with @code{STATUS='SCRATCH'}, GNU Fortran tries to
+create the file in one of the potential directories by testing each
+directory in the order below.
+
+@enumerate
+@item
+The environment variable @env{TMPDIR}, if it exists.
+
+@item
+On the MinGW target, the directory returned by the @code{GetTempPath}
+function. Alternatively, on the Cygwin target, the @env{TMP} and
+@env{TEMP} environment variables, if they exist, in that order.
+
+@item
+The @code{P_tmpdir} macro if it is defined, otherwise the directory
+@file{/tmp}.
+@end enumerate
+
@node GFORTRAN_STDIN_UNIT
@section @env{GFORTRAN_STDIN_UNIT}---Unit number for standard input
preconnected to standard error. This must be a positive integer.
The default value is 0.
-@node GFORTRAN_USE_STDERR
-@section @env{GFORTRAN_USE_STDERR}---Send library output to standard error
-
-This environment variable controls where library output is sent.
-If the first letter is @samp{y}, @samp{Y} or @samp{1}, standard
-error is used. If the first letter is @samp{n}, @samp{N} or
-@samp{0}, standard output is used.
-
-@node GFORTRAN_TMPDIR
-@section @env{GFORTRAN_TMPDIR}---Directory for scratch files
-
-This environment variable controls where scratch files are
-created. If this environment variable is missing,
-GNU Fortran searches for the environment variable @env{TMP}. If
-this is also missing, the default is @file{/tmp}.
-
@node GFORTRAN_UNBUFFERED_ALL
-@section @env{GFORTRAN_UNBUFFERED_ALL}---Don't buffer I/O on all units
+@section @env{GFORTRAN_UNBUFFERED_ALL}---Do not buffer I/O on all units
This environment variable controls whether all I/O is unbuffered. If
the first letter is @samp{y}, @samp{Y} or @samp{1}, all I/O is
-unbuffered. This will slow down small sequential reads and writes. If
+unbuffered. This will slow down small sequential reads and writes. If
the first letter is @samp{n}, @samp{N} or @samp{0}, I/O is buffered.
This is the default.
@node GFORTRAN_UNBUFFERED_PRECONNECTED
-@section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Don't buffer I/O on preconnected units
+@section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Do not buffer I/O on preconnected units
The environment variable named @env{GFORTRAN_UNBUFFERED_PRECONNECTED} controls
-whether I/O on a preconnected unit (i.e.@: STDOUT or STDERR) is unbuffered. If
-the first letter is @samp{y}, @samp{Y} or @samp{1}, I/O is unbuffered. This
+whether I/O on a preconnected unit (i.e.@: STDOUT or STDERR) is unbuffered. If
+the first letter is @samp{y}, @samp{Y} or @samp{1}, I/O is unbuffered. This
will slow down small sequential reads and writes. If the first letter
is @samp{n}, @samp{N} or @samp{0}, I/O is buffered. This is the default.
If the first letter is @samp{y}, @samp{Y} or @samp{1}, filename and
line numbers for runtime errors are printed. If the first letter is
-@samp{n}, @samp{N} or @samp{0}, don't print filename and line numbers
-for runtime errors. The default is to print the location.
+@samp{n}, @samp{N} or @samp{0}, do not print filename and line numbers
+for runtime errors. The default is to print the location.
@node GFORTRAN_OPTIONAL_PLUS
@section @env{GFORTRAN_OPTIONAL_PLUS}---Print leading + where permitted
a plus sign is printed
where permitted by the Fortran standard. If the first letter
is @samp{n}, @samp{N} or @samp{0}, a plus sign is not printed
-in most cases. Default is not to print plus signs.
-
-@node GFORTRAN_DEFAULT_RECL
-@section @env{GFORTRAN_DEFAULT_RECL}---Default record length for new files
-
-This environment variable specifies the default record length, in
-bytes, for files which are opened without a @code{RECL} tag in the
-@code{OPEN} statement. This must be a positive integer. The
-default value is 1073741824 bytes (1 GB).
+in most cases. Default is not to print plus signs.
@node GFORTRAN_LIST_SEPARATOR
@section @env{GFORTRAN_LIST_SEPARATOR}---Separator for list output
Examples of values for @env{GFORTRAN_CONVERT_UNIT} are:
@itemize @w{}
@item @code{'big_endian'} Do all unformatted I/O in big_endian mode.
-@item @code{'little_endian;native:10-20,25'} Do all unformatted I/O
+@item @code{'little_endian;native:10-20,25'} Do all unformatted I/O
in little_endian mode, except for units 10 to 20 and 25, which are in
native format.
@item @code{'10-20'} Units 10 to 20 are big-endian, the rest is native.
open statement}. This is to give control over data formats to
users who do not have the source code of their program available.
-@node GFORTRAN_ERROR_DUMPCORE
-@section @env{GFORTRAN_ERROR_DUMPCORE}---Dump core on run-time errors
-
-If the @env{GFORTRAN_ERROR_DUMPCORE} variable is set to
-@samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
-then library run-time errors cause core dumps. To disable the core
-dumps, set the variable to @samp{n}, @samp{N}, @samp{0}. Default
-is not to core dump unless the @option{-fdump-core} compile option
-was used.
-
@node GFORTRAN_ERROR_BACKTRACE
@section @env{GFORTRAN_ERROR_BACKTRACE}---Show backtrace on run-time errors
-If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to
-@samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
-then a backtrace is printed when a run-time error occurs.
-To disable the backtracing, set the variable to
-@samp{n}, @samp{N}, @samp{0}. Default is not to print a backtrace
-unless the @option{-fbacktrace} compile option
-was used.
+If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to @samp{y},
+@samp{Y} or @samp{1} (only the first letter is relevant) then a
+backtrace is printed when a serious run-time error occurs. To disable
+the backtracing, set the variable to @samp{n}, @samp{N}, @samp{0}.
+Default is to print a backtrace unless the @option{-fno-backtrace}
+compile option was used.
+
+@node GFORTRAN_FORMATTED_BUFFER_SIZE
+@section @env{GFORTRAN_FORMATTED_BUFFER_SIZE}---Set buffer size for formatted I/O
+
+The @env{GFORTRAN_FORMATTED_BUFFER_SIZE} environment variable
+specifies buffer size in bytes to be used for formatted output.
+The default value is 8192.
+
+@node GFORTRAN_UNFORMATTED_BUFFER_SIZE
+@section @env{GFORTRAN_UNFORMATTED_BUFFER_SIZE}---Set buffer size for unformatted I/O
+
+The @env{GFORTRAN_UNFORMATTED_BUFFER_SIZE} environment variable
+specifies buffer size in bytes to be used for unformatted output.
+The default value is 131072.
@c =====================================================================
@c PART II: LANGUAGE REFERENCE
@end tex
@c ---------------------------------------------------------------------
-@c Fortran 2003 and 2008 Status
+@c Fortran standards status
@c ---------------------------------------------------------------------
-@node Fortran 2003 and 2008 status
-@chapter Fortran 2003 and 2008 Status
+@node Fortran standards status
+@chapter Fortran standards status
@menu
* Fortran 2003 status::
* Fortran 2008 status::
+* Fortran 2018 status::
@end menu
@node Fortran 2003 status
@section Fortran 2003 status
-Although GNU Fortran focuses on implementing the Fortran 95
-standard for the time being, a few Fortran 2003 features are currently
-available.
+GNU Fortran supports several Fortran 2003 features; an incomplete
+list can be found below. See also the
+@uref{https://gcc.gnu.org/wiki/Fortran2003, wiki page} about Fortran 2003.
@itemize
-@item
-Intrinsics @code{command_argument_count}, @code{get_command},
-@code{get_command_argument}, @code{get_environment_variable}, and
-@code{move_alloc}.
+@item Procedure pointers including procedure-pointer components with
+@code{PASS} attribute.
+
+@item Procedures which are bound to a derived type (type-bound procedures)
+including @code{PASS}, @code{PROCEDURE} and @code{GENERIC}, and
+operators bound to a type.
+
+@item Abstract interfaces and type extension with the possibility to
+override type-bound procedures or to have deferred binding.
+
+@item Polymorphic entities (``@code{CLASS}'') for derived types and unlimited
+polymorphism (``@code{CLASS(*)}'') -- including @code{SAME_TYPE_AS},
+@code{EXTENDS_TYPE_OF} and @code{SELECT TYPE} for scalars and arrays and
+finalization.
+
+@item Generic interface names, which have the same name as derived types,
+are now supported. This allows one to write constructor functions. Note
+that Fortran does not support static constructor functions. For static
+variables, only default initialization or structure-constructor
+initialization are available.
+
+@item The @code{ASSOCIATE} construct.
-@item
+@item Interoperability with C including enumerations,
+
+@item In structure constructors the components with default values may be
+omitted.
+
+@item Extensions to the @code{ALLOCATE} statement, allowing for a
+type-specification with type parameter and for allocation and initialization
+from a @code{SOURCE=} expression; @code{ALLOCATE} and @code{DEALLOCATE}
+optionally return an error message string via @code{ERRMSG=}.
+
+@item Reallocation on assignment: If an intrinsic assignment is
+used, an allocatable variable on the left-hand side is automatically allocated
+(if unallocated) or reallocated (if the shape is different). Currently, scalar
+deferred character length left-hand sides are correctly handled but arrays
+are not yet fully implemented.
+
+@item Deferred-length character variables and scalar deferred-length character
+components of derived types are supported. (Note that array-valued components
+are not yet implemented.)
+
+@item Transferring of allocations via @code{MOVE_ALLOC}.
+
+@item The @code{PRIVATE} and @code{PUBLIC} attributes may be given individually
+to derived-type components.
+
+@item In pointer assignments, the lower bound may be specified and
+the remapping of elements is supported.
+
+@item For pointers an @code{INTENT} may be specified which affect the
+association status not the value of the pointer target.
+
+@item Intrinsics @code{command_argument_count}, @code{get_command},
+@code{get_command_argument}, and @code{get_environment_variable}.
+
+@item Support for Unicode characters (ISO 10646) and UTF-8, including
+the @code{SELECTED_CHAR_KIND} and @code{NEW_LINE} intrinsic functions.
+
+@item Support for binary, octal and hexadecimal (BOZ) constants in the
+intrinsic functions @code{INT}, @code{REAL}, @code{CMPLX} and @code{DBLE}.
+
+@item Support for namelist variables with allocatable and pointer
+attribute and nonconstant length type parameter.
+
+@item
@cindex array, constructors
@cindex @code{[...]}
-Array constructors using square brackets. That is, @code{[...]} rather
-than @code{(/.../)}.
+Array constructors using square brackets. That is, @code{[...]} rather
+than @code{(/.../)}. Type-specification for array constructors like
+@code{(/ some-type :: ... /)}.
+
+@item Extensions to the specification and initialization expressions,
+including the support for intrinsics with real and complex arguments.
+
+@item Support for the asynchronous input/output.
@item
@cindex @code{FLUSH} statement
@item
Namelist input/output for internal files.
+@item Minor I/O features: Rounding during formatted output, using of
+a decimal comma instead of a decimal point, setting whether a plus sign
+should appear for positive numbers. On systems where @code{strtod} honours
+the rounding mode, the rounding mode is also supported for input.
+
@item
@cindex @code{PROTECTED} statement
@cindex statement, @code{PROTECTED}
The @code{IMPORT} statement, allowing to import
host-associated derived types.
+@item The intrinsic modules @code{ISO_FORTRAN_ENVIRONMENT} is supported,
+which contains parameters of the I/O units, storage sizes. Additionally,
+procedures for C interoperability are available in the @code{ISO_C_BINDING}
+module.
+
@item
@cindex @code{USE, INTRINSIC} statement
@cindex statement, @code{USE, INTRINSIC}
@cindex statement, @code{ISO_FORTRAN_ENV}
@code{USE} statement with @code{INTRINSIC} and @code{NON_INTRINSIC}
attribute; supported intrinsic modules: @code{ISO_FORTRAN_ENV},
-@code{OMP_LIB} and @code{OMP_LIB_KINDS}.
+@code{ISO_C_BINDING}, @code{OMP_LIB} and @code{OMP_LIB_KINDS},
+and @code{OPENACC}.
@item
Renaming of operators in the @code{USE} statement.
-@item
-@cindex ISO C Bindings
-Interoperability with C (ISO C Bindings)
-
-@item
-BOZ as argument of INT, REAL, DBLE and CMPLX.
-
@end itemize
@node Fortran 2008 status
@section Fortran 2008 status
-The next version of the Fortran standard after Fortran 2003 is currently
-being worked on by the Working Group 5 of Sub-Committee 22 of the Joint
-Technical Committee 1 of the International Organization for
-Standardization (ISO) and the International Electrotechnical Commission
-(IEC). This group is known at @uref{http://www.nag.co.uk/sc22wg5/, WG5}.
-The next revision of the Fortran standard is informally referred to as
-Fortran 2008, reflecting its planned release year. The GNU Fortran
-compiler has support for some of the new features in Fortran 2008. This
-support is based on the latest draft, available from
-@url{http://www.nag.co.uk/sc22wg5/}. However, as the final standard may
-differ from the drafts, no guarantee of backward compatibility can be
-made and you should only use it for experimental purposes.
+The latest version of the Fortran standard is ISO/IEC 1539-1:2010, informally
+known as Fortran 2008. The official version is available from International
+Organization for Standardization (ISO) or its national member organizations.
+The the final draft (FDIS) can be downloaded free of charge from
+@url{http://www.nag.co.uk/@/sc22wg5/@/links.html}. Fortran is developed by the
+Working Group 5 of Sub-Committee 22 of the Joint Technical Committee 1 of the
+International Organization for Standardization and the International
+Electrotechnical Commission (IEC). This group is known as
+@uref{http://www.nag.co.uk/sc22wg5/, WG5}.
+
+The GNU Fortran compiler supports several of the new features of Fortran 2008;
+the @uref{https://gcc.gnu.org/wiki/Fortran2008Status, wiki} has some information
+about the current Fortran 2008 implementation status. In particular, the
+following is implemented.
+
+@itemize
+@item The @option{-std=f2008} option and support for the file extensions
+@file{.f08} and @file{.F08}.
+
+@item The @code{OPEN} statement now supports the @code{NEWUNIT=} option,
+which returns a unique file unit, thus preventing inadvertent use of the
+same unit in different parts of the program.
+
+@item The @code{g0} format descriptor and unlimited format items.
+
+@item The mathematical intrinsics @code{ASINH}, @code{ACOSH}, @code{ATANH},
+@code{ERF}, @code{ERFC}, @code{GAMMA}, @code{LOG_GAMMA}, @code{BESSEL_J0},
+@code{BESSEL_J1}, @code{BESSEL_JN}, @code{BESSEL_Y0}, @code{BESSEL_Y1},
+@code{BESSEL_YN}, @code{HYPOT}, @code{NORM2}, and @code{ERFC_SCALED}.
+
+@item Using complex arguments with @code{TAN}, @code{SINH}, @code{COSH},
+@code{TANH}, @code{ASIN}, @code{ACOS}, and @code{ATAN} is now possible;
+@code{ATAN}(@var{Y},@var{X}) is now an alias for @code{ATAN2}(@var{Y},@var{X}).
+
+@item Support of the @code{PARITY} intrinsic functions.
+
+@item The following bit intrinsics: @code{LEADZ} and @code{TRAILZ} for
+counting the number of leading and trailing zero bits, @code{POPCNT} and
+@code{POPPAR} for counting the number of one bits and returning the parity;
+@code{BGE}, @code{BGT}, @code{BLE}, and @code{BLT} for bitwise comparisons;
+@code{DSHIFTL} and @code{DSHIFTR} for combined left and right shifts,
+@code{MASKL} and @code{MASKR} for simple left and right justified masks,
+@code{MERGE_BITS} for a bitwise merge using a mask, @code{SHIFTA},
+@code{SHIFTL} and @code{SHIFTR} for shift operations, and the
+transformational bit intrinsics @code{IALL}, @code{IANY} and @code{IPARITY}.
+
+@item Support of the @code{EXECUTE_COMMAND_LINE} intrinsic subroutine.
+
+@item Support for the @code{STORAGE_SIZE} intrinsic inquiry function.
+
+@item The @code{INT@{8,16,32@}} and @code{REAL@{32,64,128@}} kind type
+parameters and the array-valued named constants @code{INTEGER_KINDS},
+@code{LOGICAL_KINDS}, @code{REAL_KINDS} and @code{CHARACTER_KINDS} of
+the intrinsic module @code{ISO_FORTRAN_ENV}.
+
+@item The module procedures @code{C_SIZEOF} of the intrinsic module
+@code{ISO_C_BINDINGS} and @code{COMPILER_VERSION} and @code{COMPILER_OPTIONS}
+of @code{ISO_FORTRAN_ENV}.
+
+@item Coarray support for serial programs with @option{-fcoarray=single} flag
+and experimental support for multiple images with the @option{-fcoarray=lib}
+flag.
+
+@item Submodules are supported. It should noted that @code{MODULEs} do not
+produce the smod file needed by the descendent @code{SUBMODULEs} unless they
+contain at least one @code{MODULE PROCEDURE} interface. The reason for this is
+that @code{SUBMODULEs} are useless without @code{MODULE PROCEDUREs}. See
+http://j3-fortran.org/doc/meeting/207/15-209.txt for a discussion and a draft
+interpretation. Adopting this interpretation has the advantage that code that
+does not use submodules does not generate smod files.
+
+@item The @code{DO CONCURRENT} construct is supported.
+
+@item The @code{BLOCK} construct is supported.
+
+@item The @code{STOP} and the new @code{ERROR STOP} statements now
+support all constant expressions. Both show the signals which were signaling
+at termination.
+
+@item Support for the @code{CONTIGUOUS} attribute.
+
+@item Support for @code{ALLOCATE} with @code{MOLD}.
+
+@item Support for the @code{IMPURE} attribute for procedures, which
+allows for @code{ELEMENTAL} procedures without the restrictions of
+@code{PURE}.
+
+@item Null pointers (including @code{NULL()}) and not-allocated variables
+can be used as actual argument to optional non-pointer, non-allocatable
+dummy arguments, denoting an absent argument.
+
+@item Non-pointer variables with @code{TARGET} attribute can be used as
+actual argument to @code{POINTER} dummies with @code{INTENT(IN)}.
+
+@item Pointers including procedure pointers and those in a derived
+type (pointer components) can now be initialized by a target instead
+of only by @code{NULL}.
+
+@item The @code{EXIT} statement (with construct-name) can be now be
+used to leave not only the @code{DO} but also the @code{ASSOCIATE},
+@code{BLOCK}, @code{IF}, @code{SELECT CASE} and @code{SELECT TYPE}
+constructs.
+
+@item Internal procedures can now be used as actual argument.
+
+@item Minor features: obsolesce diagnostics for @code{ENTRY} with
+@option{-std=f2008}; a line may start with a semicolon; for internal
+and module procedures @code{END} can be used instead of
+@code{END SUBROUTINE} and @code{END FUNCTION}; @code{SELECTED_REAL_KIND}
+now also takes a @code{RADIX} argument; intrinsic types are supported
+for @code{TYPE}(@var{intrinsic-type-spec}); multiple type-bound procedures
+can be declared in a single @code{PROCEDURE} statement; implied-shape
+arrays are supported for named constants (@code{PARAMETER}).
+@end itemize
+
+
+
+@node Fortran 2018 status
+@section Status of Fortran 2018 support
+
+@itemize
+@item ERROR STOP in a PURE procedure
+An @code{ERROR STOP} statement is permitted in a @code{PURE}
+procedure.
+
+@item IMPLICIT NONE with a spec-list
+Support the @code{IMPLICIT NONE} statement with an
+@code{implicit-none-spec-list}.
+
+@item Behavior of INQUIRE with the RECL= specifier
+
+The behavior of the @code{INQUIRE} statement with the @code{RECL=}
+specifier now conforms to Fortran 2018.
+
+@end itemize
+
+
+@subsection TS 29113 Status (Further Interoperability with C)
+
+GNU Fortran supports some of the new features of the Technical
+Specification (TS) 29113 on Further Interoperability of Fortran with C.
+The @uref{https://gcc.gnu.org/wiki/TS29113Status, wiki} has some information
+about the current TS 29113 implementation status. In particular, the
+following is implemented.
+
+See also @ref{Further Interoperability of Fortran with C}.
+
+@itemize
+@item The @code{OPTIONAL} attribute is allowed for dummy arguments
+of @code{BIND(C) procedures.}
+
+@item The @code{RANK} intrinsic is supported.
+
+@item GNU Fortran's implementation for variables with @code{ASYNCHRONOUS}
+attribute is compatible with TS 29113.
+
+@item Assumed types (@code{TYPE(*)}).
+
+@item Assumed-rank (@code{DIMENSION(..)}).
+
+@item ISO_Fortran_binding (now in Fortran 2018 18.4) is implemented such that
+conversion of the array descriptor for assumed type or assumed rank arrays is
+done in the library. The include file ISO_Fortran_binding.h is can be found in
+@code{~prefix/lib/gcc/$target/$version}.
+@end itemize
+
+
+
+@subsection TS 18508 Status (Additional Parallel Features)
+
+GNU Fortran supports the following new features of the Technical
+Specification 18508 on Additional Parallel Features in Fortran:
+
+@itemize
+@item The new atomic ADD, CAS, FETCH and ADD/OR/XOR, OR and XOR intrinsics.
+
+@item The @code{CO_MIN} and @code{CO_MAX} and @code{SUM} reduction intrinsics.
+And the @code{CO_BROADCAST} and @code{CO_REDUCE} intrinsic, except that those
+do not support polymorphic types or types with allocatable, pointer or
+polymorphic components.
+
+@item Events (@code{EVENT POST}, @code{EVENT WAIT}, @code{EVENT_QUERY})
+
+@item Failed images (@code{FAIL IMAGE}, @code{IMAGE_STATUS},
+@code{FAILED_IMAGES}, @code{STOPPED_IMAGES})
+
+@end itemize
+
+
+@c ---------------------------------------------------------------------
+@c Compiler Characteristics
+@c ---------------------------------------------------------------------
+
+@node Compiler Characteristics
+@chapter Compiler Characteristics
+
+This chapter describes certain characteristics of the GNU Fortran
+compiler, that are not specified by the Fortran standard, but which
+might in some way or another become visible to the programmer.
+
+@menu
+* KIND Type Parameters::
+* Internal representation of LOGICAL variables::
+* Evaluation of logical expressions::
+* MAX and MIN intrinsics with REAL NaN arguments::
+* Thread-safety of the runtime library::
+* Data consistency and durability::
+* Files opened without an explicit ACTION= specifier::
+* File operations on symbolic links::
+* File format of unformatted sequential files::
+* Asynchronous I/O::
+@end menu
+
+
+@node KIND Type Parameters
+@section KIND Type Parameters
+@cindex kind
+
+The @code{KIND} type parameters supported by GNU Fortran for the primitive
+data types are:
+
+@table @code
+
+@item INTEGER
+1, 2, 4, 8*, 16*, default: 4**
+
+@item LOGICAL
+1, 2, 4, 8*, 16*, default: 4**
+
+@item REAL
+4, 8, 10*, 16*, default: 4***
+
+@item COMPLEX
+4, 8, 10*, 16*, default: 4***
+
+@item DOUBLE PRECISION
+4, 8, 10*, 16*, default: 8***
+
+@item CHARACTER
+1, 4, default: 1
+
+@end table
+
+@noindent
+* not available on all systems @*
+** unless @option{-fdefault-integer-8} is used @*
+*** unless @option{-fdefault-real-8} is used (see @ref{Fortran Dialect Options})
+
+@noindent
+The @code{KIND} value matches the storage size in bytes, except for
+@code{COMPLEX} where the storage size is twice as much (or both real and
+imaginary part are a real value of the given size). It is recommended to use
+the @ref{SELECTED_CHAR_KIND}, @ref{SELECTED_INT_KIND} and
+@ref{SELECTED_REAL_KIND} intrinsics or the @code{INT8}, @code{INT16},
+@code{INT32}, @code{INT64}, @code{REAL32}, @code{REAL64}, and @code{REAL128}
+parameters of the @code{ISO_FORTRAN_ENV} module instead of the concrete values.
+The available kind parameters can be found in the constant arrays
+@code{CHARACTER_KINDS}, @code{INTEGER_KINDS}, @code{LOGICAL_KINDS} and
+@code{REAL_KINDS} in the @ref{ISO_FORTRAN_ENV} module. For C interoperability,
+the kind parameters of the @ref{ISO_C_BINDING} module should be used.
+
+
+@node Internal representation of LOGICAL variables
+@section Internal representation of LOGICAL variables
+@cindex logical, variable representation
+
+The Fortran standard does not specify how variables of @code{LOGICAL}
+type are represented, beyond requiring that @code{LOGICAL} variables
+of default kind have the same storage size as default @code{INTEGER}
+and @code{REAL} variables. The GNU Fortran internal representation is
+as follows.
+
+A @code{LOGICAL(KIND=N)} variable is represented as an
+@code{INTEGER(KIND=N)} variable, however, with only two permissible
+values: @code{1} for @code{.TRUE.} and @code{0} for
+@code{.FALSE.}. Any other integer value results in undefined behavior.
+
+See also @ref{Argument passing conventions} and @ref{Interoperability with C}.
+
+
+@node Evaluation of logical expressions
+@section Evaluation of logical expressions
+
+The Fortran standard does not require the compiler to evaluate all parts of an
+expression, if they do not contribute to the final result. For logical
+expressions with @code{.AND.} or @code{.OR.} operators, in particular, GNU
+Fortran will optimize out function calls (even to impure functions) if the
+result of the expression can be established without them. However, since not
+all compilers do that, and such an optimization can potentially modify the
+program flow and subsequent results, GNU Fortran throws warnings for such
+situations with the @option{-Wfunction-elimination} flag.
+
+
+@node MAX and MIN intrinsics with REAL NaN arguments
+@section MAX and MIN intrinsics with REAL NaN arguments
+@cindex MAX, MIN, NaN
+
+The Fortran standard does not specify what the result of the
+@code{MAX} and @code{MIN} intrinsics are if one of the arguments is a
+@code{NaN}. Accordingly, the GNU Fortran compiler does not specify
+that either, as this allows for faster and more compact code to be
+generated. If the programmer wishes to take some specific action in
+case one of the arguments is a @code{NaN}, it is necessary to
+explicitly test the arguments before calling @code{MAX} or @code{MIN},
+e.g. with the @code{IEEE_IS_NAN} function from the intrinsic module
+@code{IEEE_ARITHMETIC}.
+
+
+@node Thread-safety of the runtime library
+@section Thread-safety of the runtime library
+@cindex thread-safety, threads
+
+GNU Fortran can be used in programs with multiple threads, e.g.@: by
+using OpenMP, by calling OS thread handling functions via the
+@code{ISO_C_BINDING} facility, or by GNU Fortran compiled library code
+being called from a multi-threaded program.
+
+The GNU Fortran runtime library, (@code{libgfortran}), supports being
+called concurrently from multiple threads with the following
+exceptions.
+
+During library initialization, the C @code{getenv} function is used,
+which need not be thread-safe. Similarly, the @code{getenv}
+function is used to implement the @code{GET_ENVIRONMENT_VARIABLE} and
+@code{GETENV} intrinsics. It is the responsibility of the user to
+ensure that the environment is not being updated concurrently when any
+of these actions are taking place.
+
+The @code{EXECUTE_COMMAND_LINE} and @code{SYSTEM} intrinsics are
+implemented with the @code{system} function, which need not be
+thread-safe. It is the responsibility of the user to ensure that
+@code{system} is not called concurrently.
+
+For platforms not supporting thread-safe POSIX functions, further
+functionality might not be thread-safe. For details, please consult
+the documentation for your operating system.
+
+The GNU Fortran runtime library uses various C library functions that
+depend on the locale, such as @code{strtod} and @code{snprintf}. In
+order to work correctly in locale-aware programs that set the locale
+using @code{setlocale}, the locale is reset to the default ``C''
+locale while executing a formatted @code{READ} or @code{WRITE}
+statement. On targets supporting the POSIX 2008 per-thread locale
+functions (e.g. @code{newlocale}, @code{uselocale},
+@code{freelocale}), these are used and thus the global locale set
+using @code{setlocale} or the per-thread locales in other threads are
+not affected. However, on targets lacking this functionality, the
+global LC_NUMERIC locale is set to ``C'' during the formatted I/O.
+Thus, on such targets it's not safe to call @code{setlocale}
+concurrently from another thread while a Fortran formatted I/O
+operation is in progress. Also, other threads doing something
+dependent on the LC_NUMERIC locale might not work correctly if a
+formatted I/O operation is in progress in another thread.
+
+@node Data consistency and durability
+@section Data consistency and durability
+@cindex consistency, durability
+
+This section contains a brief overview of data and metadata
+consistency and durability issues when doing I/O.
+
+With respect to durability, GNU Fortran makes no effort to ensure that
+data is committed to stable storage. If this is required, the GNU
+Fortran programmer can use the intrinsic @code{FNUM} to retrieve the
+low level file descriptor corresponding to an open Fortran unit. Then,
+using e.g. the @code{ISO_C_BINDING} feature, one can call the
+underlying system call to flush dirty data to stable storage, such as
+@code{fsync} on POSIX, @code{_commit} on MingW, or @code{fcntl(fd,
+F_FULLSYNC, 0)} on Mac OS X. The following example shows how to call
+fsync:
+
+@smallexample
+ ! Declare the interface for POSIX fsync function
+ interface
+ function fsync (fd) bind(c,name="fsync")
+ use iso_c_binding, only: c_int
+ integer(c_int), value :: fd
+ integer(c_int) :: fsync
+ end function fsync
+ end interface
+
+ ! Variable declaration
+ integer :: ret
+
+ ! Opening unit 10
+ open (10,file="foo")
+
+ ! ...
+ ! Perform I/O on unit 10
+ ! ...
+
+ ! Flush and sync
+ flush(10)
+ ret = fsync(fnum(10))
+
+ ! Handle possible error
+ if (ret /= 0) stop "Error calling FSYNC"
+@end smallexample
+
+With respect to consistency, for regular files GNU Fortran uses
+buffered I/O in order to improve performance. This buffer is flushed
+automatically when full and in some other situations, e.g. when
+closing a unit. It can also be explicitly flushed with the
+@code{FLUSH} statement. Also, the buffering can be turned off with the
+@code{GFORTRAN_UNBUFFERED_ALL} and
+@code{GFORTRAN_UNBUFFERED_PRECONNECTED} environment variables. Special
+files, such as terminals and pipes, are always unbuffered. Sometimes,
+however, further things may need to be done in order to allow other
+processes to see data that GNU Fortran has written, as follows.
+
+The Windows platform supports a relaxed metadata consistency model,
+where file metadata is written to the directory lazily. This means
+that, for instance, the @code{dir} command can show a stale size for a
+file. One can force a directory metadata update by closing the unit,
+or by calling @code{_commit} on the file descriptor. Note, though,
+that @code{_commit} will force all dirty data to stable storage, which
+is often a very slow operation.
+
+The Network File System (NFS) implements a relaxed consistency model
+called open-to-close consistency. Closing a file forces dirty data and
+metadata to be flushed to the server, and opening a file forces the
+client to contact the server in order to revalidate cached
+data. @code{fsync} will also force a flush of dirty data and metadata
+to the server. Similar to @code{open} and @code{close}, acquiring and
+releasing @code{fcntl} file locks, if the server supports them, will
+also force cache validation and flushing dirty data and metadata.
+
+
+@node Files opened without an explicit ACTION= specifier
+@section Files opened without an explicit ACTION= specifier
+@cindex open, action
+
+The Fortran standard says that if an @code{OPEN} statement is executed
+without an explicit @code{ACTION=} specifier, the default value is
+processor dependent. GNU Fortran behaves as follows:
+
+@enumerate
+@item Attempt to open the file with @code{ACTION='READWRITE'}
+@item If that fails, try to open with @code{ACTION='READ'}
+@item If that fails, try to open with @code{ACTION='WRITE'}
+@item If that fails, generate an error
+@end enumerate
+
+
+@node File operations on symbolic links
+@section File operations on symbolic links
+@cindex file, symbolic link
+
+This section documents the behavior of GNU Fortran for file operations on
+symbolic links, on systems that support them.
+
+@itemize
+
+@item Results of INQUIRE statements of the ``inquire by file'' form will
+relate to the target of the symbolic link. For example,
+@code{INQUIRE(FILE="foo",EXIST=ex)} will set @var{ex} to @var{.true.} if
+@var{foo} is a symbolic link pointing to an existing file, and @var{.false.}
+if @var{foo} points to an non-existing file (``dangling'' symbolic link).
+
+@item Using the @code{OPEN} statement with a @code{STATUS="NEW"} specifier
+on a symbolic link will result in an error condition, whether the symbolic
+link points to an existing target or is dangling.
+
+@item If a symbolic link was connected, using the @code{CLOSE} statement
+with a @code{STATUS="DELETE"} specifier will cause the symbolic link itself
+to be deleted, not its target.
+
+@end itemize
+
+@node File format of unformatted sequential files
+@section File format of unformatted sequential files
+@cindex file, unformatted sequential
+@cindex unformatted sequential
+@cindex sequential, unformatted
+@cindex record marker
+@cindex subrecord
+
+Unformatted sequential files are stored as logical records using
+record markers. Each logical record consists of one of more
+subrecords.
+
+Each subrecord consists of a leading record marker, the data written
+by the user program, and a trailing record marker. The record markers
+are four-byte integers by default, and eight-byte integers if the
+@option{-fmax-subrecord-length=8} option (which exists for backwards
+compability only) is in effect.
+
+The representation of the record markers is that of unformatted files
+given with the @option{-fconvert} option, the @ref{CONVERT specifier}
+in an open statement or the @ref{GFORTRAN_CONVERT_UNIT} environment
+variable.
+
+The maximum number of bytes of user data in a subrecord is 2147483639
+(2 GiB - 9) for a four-byte record marker. This limit can be lowered
+with the @option{-fmax-subrecord-length} option, altough this is
+rarely useful. If the length of a logical record exceeds this limit,
+the data is distributed among several subrecords.
+
+The absolute of the number stored in the record markers is the number
+of bytes of user data in the corresponding subrecord. If the leading
+record marker of a subrecord contains a negative number, another
+subrecord follows the current one. If the trailing record marker
+contains a negative number, then there is a preceding subrecord.
+
+In the most simple case, with only one subrecord per logical record,
+both record markers contain the number of bytes of user data in the
+record.
+
+The format for unformatted sequential data can be duplicated using
+unformatted stream, as shown in the example program for an unformatted
+record containing a single subrecord:
+
+@smallexample
+program main
+ use iso_fortran_env, only: int32
+ implicit none
+ integer(int32) :: i
+ real, dimension(10) :: a, b
+ call random_number(a)
+ open (10,file='test.dat',form='unformatted',access='stream')
+ inquire (iolength=i) a
+ write (10) i, a, i
+ close (10)
+ open (10,file='test.dat',form='unformatted')
+ read (10) b
+ if (all (a == b)) print *,'success!'
+end program main
+@end smallexample
+
+@node Asynchronous I/O
+@section Asynchronous I/O
+@cindex input/output, asynchronous
+@cindex asynchronous I/O
+
+Asynchronous I/O is supported if the program is linked against the
+POSIX thread library. If that is not the case, all I/O is performed
+as synchronous. On systems which do not support pthread condition
+variables, such as AIX, I/O is also performed as synchronous.
+
+On some systems, such as Darwin or Solaris, the POSIX thread library
+is always linked in, so asynchronous I/O is always performed. On other
+sytems, such as Linux, it is necessary to specify @option{-pthread},
+@option{-lpthread} or @option{-fopenmp} during the linking step.
@c ---------------------------------------------------------------------
@c Extensions
@section Extensions implemented in GNU Fortran
@cindex extensions, implemented
-GNU Fortran implements a number of extensions over standard
-Fortran. This chapter contains information on their syntax and
-meaning. There are currently two categories of GNU Fortran
-extensions, those that provide functionality beyond that provided
-by any standard, and those that are supported by GNU Fortran
-purely for backward compatibility with legacy compilers. By default,
-@option{-std=gnu} allows the compiler to accept both types of
-extensions, but to warn about the use of the latter. Specifying
-either @option{-std=f95}, @option{-std=f2003} or @option{-std=f2008}
-disables both types of extensions, and @option{-std=legacy} allows both
-without warning.
+GNU Fortran implements a number of extensions over standard Fortran.
+This chapter contains information on their syntax and meaning. There
+are currently two categories of GNU Fortran extensions, those that
+provide functionality beyond that provided by any standard, and those
+that are supported by GNU Fortran purely for backward compatibility
+with legacy compilers. By default, @option{-std=gnu} allows the
+compiler to accept both types of extensions, but to warn about the use
+of the latter. Specifying either @option{-std=f95},
+@option{-std=f2003}, @option{-std=f2008}, or @option{-std=f2018}
+disables both types of extensions, and @option{-std=legacy} allows
+both without warning. The special compile flag @option{-fdec} enables
+additional compatibility extensions along with those enabled by
+@option{-std=legacy}.
@menu
* Old-style kind specifications::
* X format descriptor without count field::
* Commas in FORMAT specifications::
* Missing period in FORMAT specifications::
+* Default widths for F@comma{} G and I format descriptors::
* I/O item lists::
+* @code{Q} exponent-letter::
* BOZ literal constants::
* Real array indices::
* Unary operators::
* Implicitly convert LOGICAL and INTEGER values::
* Hollerith constants support::
+* Character conversion::
* Cray pointers::
* CONVERT specifier::
* OpenMP::
+* OpenACC::
* Argument list functions::
+* Read/Write after EOF marker::
+* STRUCTURE and RECORD::
+* UNION and MAP::
+* Type variants for integer intrinsics::
+* AUTOMATIC and STATIC attributes::
+* Extended math intrinsics::
+* Form feed as whitespace::
+* TYPE as an alias for PRINT::
+* %LOC as an rvalue::
+* .XOR. operator::
+* Bitwise logical operators::
+* Extended I/O specifiers::
+* Legacy PARAMETER statements::
+* Default exponents::
@end menu
@node Old-style kind specifications
@subsection Old-style kind specifications
@cindex kind, old-style
-GNU Fortran allows old-style kind specifications in declarations. These
+GNU Fortran allows old-style kind specifications in declarations. These
look like:
@smallexample
TYPESPEC*size x,y,z
It should be noted that the default terminator is @samp{/} rather than
@samp{&END}.
-Querying of the namelist when inputting from stdin. After at least
+Querying of the namelist when inputting from stdin. After at least
one space, entering @samp{?} sends to stdout the namelist name and the names of
the variables in the namelist:
@smallexample
END PROGRAM test_print
@end smallexample
-Expanded namelist reads are permitted. This causes an error if
+Expanded namelist reads are permitted. This causes an error if
@option{-std=f95} is used. In the following example, the first element
of the array will be given the value 0.00 and the two succeeding
elements will be given the values 1.00 and 2.00.
/
@end smallexample
+When writing a namelist, if no @code{DELIM=} is specified, by default a
+double quote is used to delimit character strings. If -std=F95, F2003,
+or F2008, etc, the delim status is set to 'none'. Defaulting to
+quotes ensures that namelists with character strings can be subsequently
+read back in accurately.
+
@node X format descriptor without count field
@subsection @code{X} format descriptor without count field
To support legacy codes, GNU Fortran allows the comma separator
to be omitted immediately before and after character string edit
-descriptors in @code{FORMAT} statements.
+descriptors in @code{FORMAT} statements. A comma with no following format
+decriptor is permited if the @option{-fdec-blank-format-item} is given on
+the command line. This is considered non-conforming code and is
+discouraged.
@smallexample
PRINT 10, 2, 3
10 FORMAT ('FOO='I1' BAR='I2)
+ print 20, 5, 6
+20 FORMAT (I3, I3,)
@end smallexample
10 FORMAT ('F4')
@end smallexample
+@node Default widths for F@comma{} G and I format descriptors
+@subsection Default widths for @code{F}, @code{G} and @code{I} format descriptors
+
+To support legacy codes, GNU Fortran allows width to be omitted from format
+specifications if and only if @option{-fdec-format-defaults} is given on the
+command line. Default widths will be used. This is considered non-conforming
+code and is discouraged.
+
+@smallexample
+ REAL :: value1
+ INTEGER :: value2
+ WRITE(*,10) value1, value1, value2
+10 FORMAT ('F, G, I')
+@end smallexample
+
+
@node I/O item lists
@subsection I/O item lists
@cindex I/O item lists
of the @code{READ} statement, and the output item lists of the
@code{WRITE} and @code{PRINT} statements, to start with a comma.
+@node @code{Q} exponent-letter
+@subsection @code{Q} exponent-letter
+@cindex @code{Q} exponent-letter
+
+GNU Fortran accepts real literal constants with an exponent-letter
+of @code{Q}, for example, @code{1.23Q45}. The constant is interpreted
+as a @code{REAL(16)} entity on targets that support this type. If
+the target does not support @code{REAL(16)} but has a @code{REAL(10)}
+type, then the real-literal-constant will be interpreted as a
+@code{REAL(10)} entity. In the absence of @code{REAL(16)} and
+@code{REAL(10)}, an error will occur.
+
@node BOZ literal constants
@subsection BOZ literal constants
@cindex BOZ literal constants
Besides decimal constants, Fortran also supports binary (@code{b}),
-octal (@code{o}) and hexadecimal (@code{z}) integer constants. The
+octal (@code{o}) and hexadecimal (@code{z}) integer constants. The
syntax is: @samp{prefix quote digits quote}, were the prefix is
either @code{b}, @code{o} or @code{z}, quote is either @code{'} or
-@code{"} and the digits are for binary @code{0} or @code{1}, for
-octal between @code{0} and @code{7}, and for hexadecimal between
-@code{0} and @code{F}. (Example: @code{b'01011101'}.)
-
-Up to Fortran 95, BOZ literals were only allowed to initialize
-integer variables in DATA statements. Since Fortran 2003 BOZ literals
-are also allowed as argument of @code{REAL}, @code{DBLE}, @code{INT}
-and @code{CMPLX}; the result is the same as if the integer BOZ
-literal had been converted by @code{TRANSFER} to, respectively,
-@code{real}, @code{double precision}, @code{integer} or @code{complex}.
-As GNU Fortran extension the intrinsic procedures @code{FLOAT},
-@code{DFLOAT}, @code{COMPLEX} and @code{DCMPLX} are treated alike.
-
-As an extension, GNU Fortran allows hexadecimal BOZ literal constants to
-be specified using the @code{X} prefix, in addition to the standard
-@code{Z} prefix. The BOZ literal can also be specified by adding a
-suffix to the string, for example, @code{Z'ABC'} and @code{'ABC'Z} are
-equivalent.
-
-Furthermore, GNU Fortran allows using BOZ literal constants outside
-DATA statements and the four intrinsic functions allowed by Fortran 2003.
-In DATA statements, in direct assignments, where the right-hand side
-only contains a BOZ literal constant, and for old-style initializers of
-the form @code{integer i /o'0173'/}, the constant is transferred
-as if @code{TRANSFER} had been used; for @code{COMPLEX} numbers, only
-the real part is initialized unless @code{CMPLX} is used. In all other
-cases, the BOZ literal constant is converted to an @code{INTEGER} value with
-the largest decimal representation. This value is then converted
-numerically to the type and kind of the variable in question.
-(For instance @code{real :: r = b'0000001' + 1} initializes @code{r}
-with @code{2.0}.) As different compilers implement the extension
-differently, one should be careful when doing bitwise initialization
-of non-integer variables.
-
-Note that initializing an @code{INTEGER} variable with a statement such
-as @code{DATA i/Z'FFFFFFFF'/} will give an integer overflow error rather
-than the desired result of @math{-1} when @code{i} is a 32-bit integer
-on a system that supports 64-bit integers. The @samp{-fno-range-check}
-option can be used as a workaround for legacy code that initializes
-integers in this manner.
+@code{"} and the digits are @code{0} or @code{1} for binary,
+between @code{0} and @code{7} for octal, and between @code{0} and
+@code{F} for hexadecimal. (Example: @code{b'01011101'}.)
+
+Up to Fortran 95, BOZ literal constants were only allowed to initialize
+integer variables in DATA statements. Since Fortran 2003 BOZ literal
+constants are also allowed as actual arguments to the @code{REAL},
+@code{DBLE}, @code{INT} and @code{CMPLX} intrinsic functions.
+The BOZ literal constant is simply a string of bits, which is padded
+or truncated as needed, during conversion to a numeric type. The
+Fortran standard states that the treatment of the sign bit is processor
+dependent. Gfortran interprets the sign bit as a user would expect.
+
+As a deprecated extension, GNU Fortran allows hexadecimal BOZ literal
+constants to be specified using the @code{X} prefix. That the BOZ literal
+constant can also be specified by adding a suffix to the string, for
+example, @code{Z'ABC'} and @code{'ABC'X} are equivalent. Additionally,
+as extension, BOZ literals are permitted in some contexts outside of
+@code{DATA} and the intrinsic functions listed in the Fortran standard.
+Use @option{-fallow-invalid-boz} to enable the extension.
@node Real array indices
@subsection Real array indices
@subsection Hollerith constants support
@cindex Hollerith constants
-GNU Fortran supports Hollerith constants in assignments, function
-arguments, and @code{DATA} and @code{ASSIGN} statements. A Hollerith
-constant is written as a string of characters preceded by an integer
-constant indicating the character count, and the letter @code{H} or
+GNU Fortran supports Hollerith constants in assignments, @code{DATA}
+statements, function and subroutine arguments. A Hollerith constant is
+written as a string of characters preceded by an integer constant
+indicating the character count, and the letter @code{H} or
@code{h}, and stored in bytewise fashion in a numeric (@code{INTEGER},
-@code{REAL}, or @code{complex}) or @code{LOGICAL} variable. The
-constant will be padded or truncated to fit the size of the variable in
-which it is stored.
+@code{REAL}, or @code{COMPLEX}), @code{LOGICAL} or @code{CHARACTER} variable.
+The constant will be padded with spaces or truncated to fit the size of
+the variable in which it is stored.
Examples of valid uses of Hollerith constants:
@smallexample
call foo (4h abc)
@end smallexample
-Invalid Hollerith constants examples:
+Examples of Hollerith constants:
@smallexample
integer*4 a
+ a = 0H ! Invalid, at least one character is needed.
+ a = 4HAB12 ! Valid
a = 8H12345678 ! Valid, but the Hollerith constant will be truncated.
- a = 0H ! At least one character is needed.
+ a = 3Hxyz ! Valid, but the Hollerith constant will be padded.
@end smallexample
In general, Hollerith constants were used to provide a rudimentary
with a given byte sequence. In these cases, the same result can be
obtained by using the @code{TRANSFER} statement, as in this example.
@smallexample
- INTEGER(KIND=4) :: a
- a = TRANSFER ("abcd", a) ! equivalent to: a = 4Habcd
+ integer(kind=4) :: a
+ a = transfer ("abcd", a) ! equivalent to: a = 4Habcd
+@end smallexample
+
+The use of the @option{-fdec} option extends support of Hollerith constants
+to comparisons:
+@smallexample
+ integer*4 a
+ a = 4hABCD
+ if (a .ne. 4habcd) then
+ write(*,*) "no match"
+ end if
+@end smallexample
+
+Supported types are numeric (@code{INTEGER}, @code{REAL}, or @code{COMPLEX}),
+and @code{CHARACTER}.
+
+@node Character conversion
+@subsection Character conversion
+@cindex conversion, to character
+
+Allowing character literals to be used in a similar way to Hollerith constants
+is a non-standard extension. This feature is enabled using
+-fdec-char-conversions and only applies to character literals of @code{kind=1}.
+
+Character literals can be used in @code{DATA} statements and assignments with
+numeric (@code{INTEGER}, @code{REAL}, or @code{COMPLEX}) or @code{LOGICAL}
+variables. Like Hollerith constants they are copied byte-wise fashion. The
+constant will be padded with spaces or truncated to fit the size of the
+variable in which it is stored.
+
+Examples:
+@smallexample
+ integer*4 x
+ data x / 'abcd' /
+
+ x = 'A' ! Will be padded.
+ x = 'ab1234' ! Will be truncated.
@end smallexample
pointer ( <pointer1> , <pointee1> ), ( <pointer2> , <pointee2> ), ...
@end smallexample
The pointer is an integer that is intended to hold a memory address.
-The pointee may be an array or scalar. A pointee can be an assumed
-size array---that is, the last dimension may be left unspecified by
-using a @code{*} in place of a value---but a pointee cannot be an
-assumed shape array. No space is allocated for the pointee.
+The pointee may be an array or scalar.
+If an assumed-size array is permitted within the scoping unit, a
+pointee can be an assumed-size array.
+That is, the last dimension may be left unspecified by using a @code{*}
+in place of a value. A pointee cannot be an assumed shape array.
+No space is allocated for the pointee.
The pointee may have its type declared before or after the pointer
statement, and its array specification (if any) may be declared
real pointee(10)
pointer (ipt, pointee)
ipt = loc (target)
- ipt = ipt + 1
+ ipt = ipt + 1
@end smallexample
The last statement does not set @code{ipt} to the address of
@code{target(1)}, as it would in C pointer arithmetic. Adding @code{1}
ipt = loc(target)
@end smallexample
As long as @code{ipt} remains unchanged, @code{iarr} is now an alias for
-@code{target}. The optimizer, however, will not detect this aliasing, so
+@code{target}. The optimizer, however, will not detect this aliasing, so
it is unsafe to use @code{iarr} and @code{target} simultaneously. Using
a pointee in any way that violates the Fortran aliasing rules or
-assumptions is illegal. It is the user's responsibility to avoid doing
+assumptions is illegal. It is the user's responsibility to avoid doing
this; the compiler works under the assumption that no such aliasing
occurs.
There are a number of restrictions on the attributes that can be applied
to Cray pointers and pointees. Pointees may not have the
@code{ALLOCATABLE}, @code{INTENT}, @code{OPTIONAL}, @code{DUMMY},
-@code{TARGET}, @code{INTRINSIC}, or @code{POINTER} attributes. Pointers
+@code{TARGET}, @code{INTRINSIC}, or @code{POINTER} attributes. Pointers
may not have the @code{DIMENSION}, @code{POINTER}, @code{TARGET},
-@code{ALLOCATABLE}, @code{EXTERNAL}, or @code{INTRINSIC} attributes.
-Pointees may not occur in more than one pointer statement. A pointee
-cannot be a pointer. Pointees cannot occur in equivalence, common, or
-data statements.
+@code{ALLOCATABLE}, @code{EXTERNAL}, or @code{INTRINSIC} attributes, nor
+may they be function results. Pointees may not occur in more than one
+pointer statement. A pointee cannot be a pointer. Pointees cannot occur
+in equivalence, common, or data statements.
A Cray pointer may also point to a function or a subroutine. For
example, the following excerpt is valid:
@cindex OpenMP
OpenMP (Open Multi-Processing) is an application programming
-interface (API) that supports multi-platform shared memory
-multiprocessing programming in C/C++ and Fortran on many
+interface (API) that supports multi-platform shared memory
+multiprocessing programming in C/C++ and Fortran on many
architectures, including Unix and Microsoft Windows platforms.
It consists of a set of compiler directives, library routines,
and environment variables that influence run-time behavior.
-GNU Fortran strives to be compatible to the
-@uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,
-OpenMP Application Program Interface v2.5}.
+GNU Fortran strives to be compatible to the
+@uref{http://openmp.org/wp/openmp-specifications/,
+OpenMP Application Program Interface v4.5}.
To enable the processing of the OpenMP directive @code{!$omp} in
free-form source code; the @code{c$omp}, @code{*$omp} and @code{!$omp}
directives in fixed form; the @code{!$} conditional compilation sentinels
in free form; and the @code{c$}, @code{*$} and @code{!$} sentinels
in fixed form, @command{gfortran} needs to be invoked with the
-@option{-fopenmp}. This also arranges for automatic linking of the
-GNU OpenMP runtime library @ref{Top,,libgomp,libgomp,GNU OpenMP
-runtime library}.
+@option{-fopenmp}. This also arranges for automatic linking of the
+GNU Offloading and Multi Processing Runtime Library
+@ref{Top,,libgomp,libgomp,GNU Offloading and Multi Processing Runtime
+Library}.
The OpenMP Fortran runtime library routines are provided both in a
form of a Fortran 90 module named @code{omp_lib} and in a form of
@itemize
@item
@option{-fopenmp} implies @option{-frecursive}, i.e., all local arrays
-will be allocated on the stack. When porting existing code to OpenMP,
+will be allocated on the stack. When porting existing code to OpenMP,
this may lead to surprising results, especially to segmentation faults
if the stacksize is limited.
@item
-On glibc-based systems, OpenMP enabled applications can not be statically
-linked due to limitations of the underlying pthreads-implementation. It
-might be possible to get a working solution if
+On glibc-based systems, OpenMP enabled applications cannot be statically
+linked due to limitations of the underlying pthreads-implementation. It
+might be possible to get a working solution if
@command{-Wl,--whole-archive -lpthread -Wl,--no-whole-archive} is added
-to the command line. However, this is not supported by @command{gcc} and
+to the command line. However, this is not supported by @command{gcc} and
thus not recommended.
@end itemize
+@node OpenACC
+@subsection OpenACC
+@cindex OpenACC
+
+OpenACC is an application programming interface (API) that supports
+offloading of code to accelerator devices. It consists of a set of
+compiler directives, library routines, and environment variables that
+influence run-time behavior.
+
+GNU Fortran strives to be compatible to the
+@uref{http://www.openacc.org/, OpenACC Application Programming
+Interface v2.6}.
+
+To enable the processing of the OpenACC directive @code{!$acc} in
+free-form source code; the @code{c$acc}, @code{*$acc} and @code{!$acc}
+directives in fixed form; the @code{!$} conditional compilation
+sentinels in free form; and the @code{c$}, @code{*$} and @code{!$}
+sentinels in fixed form, @command{gfortran} needs to be invoked with
+the @option{-fopenacc}. This also arranges for automatic linking of
+the GNU Offloading and Multi Processing Runtime Library
+@ref{Top,,libgomp,libgomp,GNU Offloading and Multi Processing Runtime
+Library}.
+
+The OpenACC Fortran runtime library routines are provided both in a
+form of a Fortran 90 module named @code{openacc} and in a form of a
+Fortran @code{include} file named @file{openacc_lib.h}.
+
@node Argument list functions
@subsection Argument list functions @code{%VAL}, @code{%REF} and @code{%LOC}
@cindex argument list functions
@cindex @code{%REF}
@cindex @code{%LOC}
-GNU Fortran supports argument list functions @code{%VAL}, @code{%REF}
-and @code{%LOC} statements, for backward compatibility with g77.
-It is recommended that these should be used only for code that is
-accessing facilities outside of GNU Fortran, such as operating system
-or windowing facilities. It is best to constrain such uses to isolated
-portions of a program--portions that deal specifically and exclusively
-with low-level, system-dependent facilities. Such portions might well
-provide a portable interface for use by the program as a whole, but are
-themselves not portable, and should be thoroughly tested each time they
+GNU Fortran supports argument list functions @code{%VAL}, @code{%REF}
+and @code{%LOC} statements, for backward compatibility with g77.
+It is recommended that these should be used only for code that is
+accessing facilities outside of GNU Fortran, such as operating system
+or windowing facilities. It is best to constrain such uses to isolated
+portions of a program--portions that deal specifically and exclusively
+with low-level, system-dependent facilities. Such portions might well
+provide a portable interface for use by the program as a whole, but are
+themselves not portable, and should be thoroughly tested each time they
are rebuilt using a new compiler or version of a compiler.
-@code{%VAL} passes a scalar argument by value, @code{%REF} passes it by
-reference and @code{%LOC} passes its memory location. Since gfortran
-already passes scalar arguments by reference, @code{%REF} is in effect
-a do-nothing. @code{%LOC} has the same effect as a fortran pointer.
+@code{%VAL} passes a scalar argument by value, @code{%REF} passes it by
+reference and @code{%LOC} passes its memory location. Since gfortran
+already passes scalar arguments by reference, @code{%REF} is in effect
+a do-nothing. @code{%LOC} has the same effect as a Fortran pointer.
An example of passing an argument by value to a C subroutine foo.:
@smallexample
@end smallexample
For details refer to the g77 manual
-@uref{http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top}.
-
-Also, the gfortran testsuite c_by_val.f and its partner c_by_val.c are
-worth a look.
-
+@uref{https://gcc.gnu.org/@/onlinedocs/@/gcc-3.4.6/@/g77/@/index.html#Top}.
+Also, @code{c_by_val.f} and its partner @code{c_by_val.c} of the
+GNU Fortran testsuite are worth a look.
-@node Extensions not implemented in GNU Fortran
-@section Extensions not implemented in GNU Fortran
-@cindex extensions, not implemented
-
-The long history of the Fortran language, its wide use and broad
-userbase, the large number of different compiler vendors and the lack of
-some features crucial to users in the first standards have lead to the
-existence of a number of important extensions to the language. While
-some of the most useful or popular extensions are supported by the GNU
-Fortran compiler, not all existing extensions are supported. This section
-aims at listing these extensions and offering advice on how best make
-code that uses them running with the GNU Fortran compiler.
-
-@c More can be found here:
-@c -- http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/Missing-Features.html
-@c -- the list of fortran and libgfortran bugs closed as WONTFIX:
-@c http://tinyurl.com/2u4h5y
+@node Read/Write after EOF marker
+@subsection Read/Write after EOF marker
+@cindex @code{EOF}
+@cindex @code{BACKSPACE}
+@cindex @code{REWIND}
-@menu
-* STRUCTURE and RECORD::
-@c * UNION and MAP::
-* ENCODE and DECODE statements::
-@c * Expressions in FORMAT statements::
-@c * Q edit descriptor::
-@c * AUTOMATIC statement::
-@c * TYPE and ACCEPT I/O Statements::
-@c * .XOR. operator::
-@c * CARRIAGECONTROL, DEFAULTFILE, DISPOSE and RECORDTYPE I/O specifiers::
-@c * Omitted arguments in procedure call:
-@end menu
+Some legacy codes rely on allowing @code{READ} or @code{WRITE} after the
+EOF file marker in order to find the end of a file. GNU Fortran normally
+rejects these codes with a run-time error message and suggests the user
+consider @code{BACKSPACE} or @code{REWIND} to properly position
+the file before the EOF marker. As an extension, the run-time error may
+be disabled using -std=legacy.
@node STRUCTURE and RECORD
@cindex @code{STRUCTURE}
@cindex @code{RECORD}
-Structures are user-defined aggregate data types; this functionality was
-standardized in Fortran 90 with an different syntax, under the name of
-``derived types''. Here is an example of code using the non portable
-structure syntax:
+Record structures are a pre-Fortran-90 vendor extension to create
+user-defined aggregate data types. Support for record structures in GNU
+Fortran can be enabled with the @option{-fdec-structure} compile flag.
+If you have a choice, you should instead use Fortran 90's ``derived types'',
+which have a different syntax.
+
+In many cases, record structures can easily be converted to derived types.
+To convert, replace @code{STRUCTURE /}@var{structure-name}@code{/}
+by @code{TYPE} @var{type-name}. Additionally, replace
+@code{RECORD /}@var{structure-name}@code{/} by
+@code{TYPE(}@var{type-name}@code{)}. Finally, in the component access,
+replace the period (@code{.}) by the percent sign (@code{%}).
+
+Here is an example of code using the non portable record structure syntax:
@example
! Declaring a structure named ``item'' and containing three fields:
store_catalog(7)%description = "milk bottle"
store_catalog(7)%price = 1.2
-! Assignments of a whole variable don't change
+! Assignments of a whole variable do not change
store_catalog(12) = pear
print *, store_catalog(12)
@end example
+@noindent
+GNU Fortran implements STRUCTURES like derived types with the following
+rules and exceptions:
-@c @node UNION and MAP
-@c @subsection @code{UNION} and @code{MAP}
-@c @cindex @code{UNION}
-@c @cindex @code{MAP}
-@c
-@c For help writing this one, see
-@c http://www.eng.umd.edu/~nsw/ench250/fortran1.htm#UNION and
-@c http://www.tacc.utexas.edu/services/userguides/pgi/pgiws_ug/pgi32u06.htm
-
-
-@node ENCODE and DECODE statements
-@subsection @code{ENCODE} and @code{DECODE} statements
-@cindex @code{ENCODE}
-@cindex @code{DECODE}
+@itemize @bullet
+@item Structures act like derived types with the @code{SEQUENCE} attribute.
+Otherwise they may contain no specifiers.
-GNU Fortran doesn't support the @code{ENCODE} and @code{DECODE}
-statements. These statements are best replaced by @code{READ} and
-@code{WRITE} statements involving internal files (@code{CHARACTER}
-variables and arrays), which have been part of the Fortran standard since
-Fortran 77. For example, replace a code fragment like
+@item Structures may contain a special field with the name @code{%FILL}.
+This will create an anonymous component which cannot be accessed but occupies
+space just as if a component of the same type was declared in its place, useful
+for alignment purposes. As an example, the following structure will consist
+of at least sixteen bytes:
@smallexample
- INTEGER*1 LINE(80)
- REAL A, B, C
-c ... Code that sets LINE
- DECODE (80, 9000, LINE) A, B, C
- 9000 FORMAT (1X, 3(F10.5))
+structure /padded/
+ character(4) start
+ character(8) %FILL
+ character(4) end
+end structure
@end smallexample
-@noindent
-with the following:
+@item Structures may share names with other symbols. For example, the following
+is invalid for derived types, but valid for structures:
@smallexample
- CHARACTER(LEN=80) LINE
- REAL A, B, C
-c ... Code that sets LINE
- READ (UNIT=LINE, FMT=9000) A, B, C
- 9000 FORMAT (1X, 3(F10.5))
+structure /header/
+ ! ...
+end structure
+record /header/ header
@end smallexample
-Similarly, replace a code fragment like
-
+@item Structure types may be declared nested within another parent structure.
+The syntax is:
@smallexample
- INTEGER*1 LINE(80)
- REAL A, B, C
-c ... Code that sets A, B and C
- ENCODE (80, 9000, LINE) A, B, C
- 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))
+structure /type-name/
+ ...
+ structure [/<type-name>/] <field-list>
+...
@end smallexample
-@noindent
-with the following:
+The type name may be ommitted, in which case the structure type itself is
+anonymous, and other structures of the same type cannot be instantiated. The
+following shows some examples:
-@smallexample
- INTEGER*1 LINE(80)
- REAL A, B, C
-c ... Code that sets A, B and C
- WRITE (UNIT=LINE, FMT=9000) A, B, C
- 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))
-@end smallexample
+@example
+structure /appointment/
+ ! nested structure definition: app_time is an array of two 'time'
+ structure /time/ app_time (2)
+ integer(1) hour, minute
+ end structure
+ character(10) memo
+end structure
+
+! The 'time' structure is still usable
+record /time/ now
+now = time(5, 30)
+
+...
+
+structure /appointment/
+ ! anonymous nested structure definition
+ structure start, end
+ integer(1) hour, minute
+ end structure
+ character(10) memo
+end structure
+@end example
+@item Structures may contain @code{UNION} blocks. For more detail see the
+section on @ref{UNION and MAP}.
-@c ---------------------------------------------------------------------
-@c Intrinsic Procedures
-@c ---------------------------------------------------------------------
+@item Structures support old-style initialization of components, like
+those described in @ref{Old-style variable initialization}. For array
+initializers, an initializer may contain a repeat specification of the form
+@code{<literal-integer> * <constant-initializer>}. The value of the integer
+indicates the number of times to repeat the constant initializer when expanding
+the initializer list.
+@end itemize
-@include intrinsic.texi
+@node UNION and MAP
+@subsection @code{UNION} and @code{MAP}
+@cindex @code{UNION}
+@cindex @code{MAP}
+Unions are an old vendor extension which were commonly used with the
+non-standard @ref{STRUCTURE and RECORD} extensions. Use of @code{UNION} and
+@code{MAP} is automatically enabled with @option{-fdec-structure}.
-@tex
-\blankpart
-@end tex
+A @code{UNION} declaration occurs within a structure; within the definition of
+each union is a number of @code{MAP} blocks. Each @code{MAP} shares storage
+with its sibling maps (in the same union), and the size of the union is the
+size of the largest map within it, just as with unions in C. The major
+difference is that component references do not indicate which union or map the
+component is in (the compiler gets to figure that out).
-@c ---------------------------------------------------------------------
+Here is a small example:
+@smallexample
+structure /myunion/
+union
+ map
+ character(2) w0, w1, w2
+ end map
+ map
+ character(6) long
+ end map
+end union
+end structure
+
+record /myunion/ rec
+! After this assignment...
+rec.long = 'hello!'
+
+! The following is true:
+! rec.w0 === 'he'
+! rec.w1 === 'll'
+! rec.w2 === 'o!'
+@end smallexample
+
+The two maps share memory, and the size of the union is ultimately six bytes:
+
+@example
+0 1 2 3 4 5 6 Byte offset
+-------------------------------
+| | | | | | |
+-------------------------------
+
+^ W0 ^ W1 ^ W2 ^
+ \-------/ \-------/ \-------/
+
+^ LONG ^
+ \---------------------------/
+@end example
+
+Following is an example mirroring the layout of an Intel x86_64 register:
+
+@example
+structure /reg/
+ union ! U0 ! rax
+ map
+ character(16) rx
+ end map
+ map
+ character(8) rh ! rah
+ union ! U1
+ map
+ character(8) rl ! ral
+ end map
+ map
+ character(8) ex ! eax
+ end map
+ map
+ character(4) eh ! eah
+ union ! U2
+ map
+ character(4) el ! eal
+ end map
+ map
+ character(4) x ! ax
+ end map
+ map
+ character(2) h ! ah
+ character(2) l ! al
+ end map
+ end union
+ end map
+ end union
+ end map
+ end union
+end structure
+record /reg/ a
+
+! After this assignment...
+a.rx = 'AAAAAAAA.BBB.C.D'
+
+! The following is true:
+a.rx === 'AAAAAAAA.BBB.C.D'
+a.rh === 'AAAAAAAA'
+a.rl === '.BBB.C.D'
+a.ex === '.BBB.C.D'
+a.eh === '.BBB'
+a.el === '.C.D'
+a.x === '.C.D'
+a.h === '.C'
+a.l === '.D'
+@end example
+
+@node Type variants for integer intrinsics
+@subsection Type variants for integer intrinsics
+@cindex intrinsics, integer
+
+Similar to the D/C prefixes to real functions to specify the input/output
+types, GNU Fortran offers B/I/J/K prefixes to integer functions for
+compatibility with DEC programs. The types implied by each are:
+
+@example
+@code{B} - @code{INTEGER(kind=1)}
+@code{I} - @code{INTEGER(kind=2)}
+@code{J} - @code{INTEGER(kind=4)}
+@code{K} - @code{INTEGER(kind=8)}
+@end example
+
+GNU Fortran supports these with the flag @option{-fdec-intrinsic-ints}.
+Intrinsics for which prefixed versions are available and in what form are noted
+in @ref{Intrinsic Procedures}. The complete list of supported intrinsics is
+here:
+
+@multitable @columnfractions .2 .2 .2 .2 .2
+
+@headitem Intrinsic @tab B @tab I @tab J @tab K
+
+@item @code{@ref{ABS}}
+ @tab @code{BABS} @tab @code{IIABS} @tab @code{JIABS} @tab @code{KIABS}
+@item @code{@ref{BTEST}}
+ @tab @code{BBTEST} @tab @code{BITEST} @tab @code{BJTEST} @tab @code{BKTEST}
+@item @code{@ref{IAND}}
+ @tab @code{BIAND} @tab @code{IIAND} @tab @code{JIAND} @tab @code{KIAND}
+@item @code{@ref{IBCLR}}
+ @tab @code{BBCLR} @tab @code{IIBCLR} @tab @code{JIBCLR} @tab @code{KIBCLR}
+@item @code{@ref{IBITS}}
+ @tab @code{BBITS} @tab @code{IIBITS} @tab @code{JIBITS} @tab @code{KIBITS}
+@item @code{@ref{IBSET}}
+ @tab @code{BBSET} @tab @code{IIBSET} @tab @code{JIBSET} @tab @code{KIBSET}
+@item @code{@ref{IEOR}}
+ @tab @code{BIEOR} @tab @code{IIEOR} @tab @code{JIEOR} @tab @code{KIEOR}
+@item @code{@ref{IOR}}
+ @tab @code{BIOR} @tab @code{IIOR} @tab @code{JIOR} @tab @code{KIOR}
+@item @code{@ref{ISHFT}}
+ @tab @code{BSHFT} @tab @code{IISHFT} @tab @code{JISHFT} @tab @code{KISHFT}
+@item @code{@ref{ISHFTC}}
+ @tab @code{BSHFTC} @tab @code{IISHFTC} @tab @code{JISHFTC} @tab @code{KISHFTC}
+@item @code{@ref{MOD}}
+ @tab @code{BMOD} @tab @code{IMOD} @tab @code{JMOD} @tab @code{KMOD}
+@item @code{@ref{NOT}}
+ @tab @code{BNOT} @tab @code{INOT} @tab @code{JNOT} @tab @code{KNOT}
+@item @code{@ref{REAL}}
+ @tab @code{--} @tab @code{FLOATI} @tab @code{FLOATJ} @tab @code{FLOATK}
+@end multitable
+
+@node AUTOMATIC and STATIC attributes
+@subsection @code{AUTOMATIC} and @code{STATIC} attributes
+@cindex variable attributes
+@cindex @code{AUTOMATIC}
+@cindex @code{STATIC}
+
+With @option{-fdec-static} GNU Fortran supports the DEC extended attributes
+@code{STATIC} and @code{AUTOMATIC} to provide explicit specification of entity
+storage. These follow the syntax of the Fortran standard @code{SAVE} attribute.
+
+@code{STATIC} is exactly equivalent to @code{SAVE}, and specifies that
+an entity should be allocated in static memory. As an example, @code{STATIC}
+local variables will retain their values across multiple calls to a function.
+
+Entities marked @code{AUTOMATIC} will be stack automatic whenever possible.
+@code{AUTOMATIC} is the default for local variables smaller than
+@option{-fmax-stack-var-size}, unless @option{-fno-automatic} is given. This
+attribute overrides @option{-fno-automatic}, @option{-fmax-stack-var-size}, and
+blanket @code{SAVE} statements.
+
+
+Examples:
+
+@example
+subroutine f
+ integer, automatic :: i ! automatic variable
+ integer x, y ! static variables
+ save
+ ...
+endsubroutine
+@end example
+@example
+subroutine f
+ integer a, b, c, x, y, z
+ static :: x
+ save y
+ automatic z, c
+ ! a, b, c, and z are automatic
+ ! x and y are static
+endsubroutine
+@end example
+@example
+! Compiled with -fno-automatic
+subroutine f
+ integer a, b, c, d
+ automatic :: a
+ ! a is automatic; b, c, and d are static
+endsubroutine
+@end example
+
+@node Extended math intrinsics
+@subsection Extended math intrinsics
+@cindex intrinsics, math
+@cindex intrinsics, trigonometric functions
+
+GNU Fortran supports an extended list of mathematical intrinsics with the
+compile flag @option{-fdec-math} for compatability with legacy code.
+These intrinsics are described fully in @ref{Intrinsic Procedures} where it is
+noted that they are extensions and should be avoided whenever possible.
+
+Specifically, @option{-fdec-math} enables the @ref{COTAN} intrinsic, and
+trigonometric intrinsics which accept or produce values in degrees instead of
+radians. Here is a summary of the new intrinsics:
+
+@multitable @columnfractions .5 .5
+@headitem Radians @tab Degrees
+@item @code{@ref{ACOS}} @tab @code{@ref{ACOSD}}*
+@item @code{@ref{ASIN}} @tab @code{@ref{ASIND}}*
+@item @code{@ref{ATAN}} @tab @code{@ref{ATAND}}*
+@item @code{@ref{ATAN2}} @tab @code{@ref{ATAN2D}}*
+@item @code{@ref{COS}} @tab @code{@ref{COSD}}*
+@item @code{@ref{COTAN}}* @tab @code{@ref{COTAND}}*
+@item @code{@ref{SIN}} @tab @code{@ref{SIND}}*
+@item @code{@ref{TAN}} @tab @code{@ref{TAND}}*
+@end multitable
+
+* Enabled with @option{-fdec-math}.
+
+For advanced users, it may be important to know the implementation of these
+functions. They are simply wrappers around the standard radian functions, which
+have more accurate builtin versions. These functions convert their arguments
+(or results) to degrees (or radians) by taking the value modulus 360 (or 2*pi)
+and then multiplying it by a constant radian-to-degree (or degree-to-radian)
+factor, as appropriate. The factor is computed at compile-time as 180/pi (or
+pi/180).
+
+@node Form feed as whitespace
+@subsection Form feed as whitespace
+@cindex form feed whitespace
+
+Historically, legacy compilers allowed insertion of form feed characters ('\f',
+ASCII 0xC) at the beginning of lines for formatted output to line printers,
+though the Fortran standard does not mention this. GNU Fortran supports the
+interpretation of form feed characters in source as whitespace for
+compatibility.
+
+@node TYPE as an alias for PRINT
+@subsection TYPE as an alias for PRINT
+@cindex type alias print
+For compatibility, GNU Fortran will interpret @code{TYPE} statements as
+@code{PRINT} statements with the flag @option{-fdec}. With this flag asserted,
+the following two examples are equivalent:
+
+@smallexample
+TYPE *, 'hello world'
+@end smallexample
+
+@smallexample
+PRINT *, 'hello world'
+@end smallexample
+
+@node %LOC as an rvalue
+@subsection %LOC as an rvalue
+@cindex LOC
+Normally @code{%LOC} is allowed only in parameter lists. However the intrinsic
+function @code{LOC} does the same thing, and is usable as the right-hand-side of
+assignments. For compatibility, GNU Fortran supports the use of @code{%LOC} as
+an alias for the builtin @code{LOC} with @option{-std=legacy}. With this
+feature enabled the following two examples are equivalent:
+
+@smallexample
+integer :: i, l
+l = %loc(i)
+call sub(l)
+@end smallexample
+
+@smallexample
+integer :: i
+call sub(%loc(i))
+@end smallexample
+
+@node .XOR. operator
+@subsection .XOR. operator
+@cindex operators, xor
+
+GNU Fortran supports @code{.XOR.} as a logical operator with @code{-std=legacy}
+for compatibility with legacy code. @code{.XOR.} is equivalent to
+@code{.NEQV.}. That is, the output is true if and only if the inputs differ.
+
+@node Bitwise logical operators
+@subsection Bitwise logical operators
+@cindex logical, bitwise
+
+With @option{-fdec}, GNU Fortran relaxes the type constraints on
+logical operators to allow integer operands, and performs the corresponding
+bitwise operation instead. This flag is for compatibility only, and should be
+avoided in new code. Consider:
+
+@smallexample
+ INTEGER :: i, j
+ i = z'33'
+ j = z'cc'
+ print *, i .AND. j
+@end smallexample
+
+In this example, compiled with @option{-fdec}, GNU Fortran will
+replace the @code{.AND.} operation with a call to the intrinsic
+@code{@ref{IAND}} function, yielding the bitwise-and of @code{i} and @code{j}.
+
+Note that this conversion will occur if at least one operand is of integral
+type. As a result, a logical operand will be converted to an integer when the
+other operand is an integer in a logical operation. In this case,
+@code{.TRUE.} is converted to @code{1} and @code{.FALSE.} to @code{0}.
+
+Here is the mapping of logical operator to bitwise intrinsic used with
+@option{-fdec}:
+
+@multitable @columnfractions .25 .25 .5
+@headitem Operator @tab Intrinsic @tab Bitwise operation
+@item @code{.NOT.} @tab @code{@ref{NOT}} @tab complement
+@item @code{.AND.} @tab @code{@ref{IAND}} @tab intersection
+@item @code{.OR.} @tab @code{@ref{IOR}} @tab union
+@item @code{.NEQV.} @tab @code{@ref{IEOR}} @tab exclusive or
+@item @code{.EQV.} @tab @code{@ref{NOT}(@ref{IEOR})} @tab complement of exclusive or
+@end multitable
+
+@node Extended I/O specifiers
+@subsection Extended I/O specifiers
+@cindex @code{CARRIAGECONTROL}
+@cindex @code{READONLY}
+@cindex @code{SHARE}
+@cindex @code{SHARED}
+@cindex @code{NOSHARED}
+@cindex I/O specifiers
+
+GNU Fortran supports the additional legacy I/O specifiers
+@code{CARRIAGECONTROL}, @code{READONLY}, and @code{SHARE} with the
+compile flag @option{-fdec}, for compatibility.
+
+@table @code
+@item CARRIAGECONTROL
+The @code{CARRIAGECONTROL} specifier allows a user to control line
+termination settings between output records for an I/O unit. The specifier has
+no meaning for readonly files. When @code{CARRAIGECONTROL} is specified upon
+opening a unit for formatted writing, the exact @code{CARRIAGECONTROL} setting
+determines what characters to write between output records. The syntax is:
+
+@smallexample
+OPEN(..., CARRIAGECONTROL=cc)
+@end smallexample
+
+Where @emph{cc} is a character expression that evaluates to one of the
+following values:
+
+@multitable @columnfractions .2 .8
+@item @code{'LIST'} @tab One line feed between records (default)
+@item @code{'FORTRAN'} @tab Legacy interpretation of the first character (see below)
+@item @code{'NONE'} @tab No separator between records
+@end multitable
+
+With @code{CARRIAGECONTROL='FORTRAN'}, when a record is written, the first
+character of the input record is not written, and instead determines the output
+record separator as follows:
+
+@multitable @columnfractions .3 .3 .4
+@headitem Leading character @tab Meaning @tab Output separating character(s)
+@item @code{'+'} @tab Overprinting @tab Carriage return only
+@item @code{'-'} @tab New line @tab Line feed and carriage return
+@item @code{'0'} @tab Skip line @tab Two line feeds and carriage return
+@item @code{'1'} @tab New page @tab Form feed and carriage return
+@item @code{'$'} @tab Prompting @tab Line feed (no carriage return)
+@item @code{CHAR(0)} @tab Overprinting (no advance) @tab None
+@end multitable
+
+@item READONLY
+The @code{READONLY} specifier may be given upon opening a unit, and is
+equivalent to specifying @code{ACTION='READ'}, except that the file may not be
+deleted on close (i.e. @code{CLOSE} with @code{STATUS="DELETE"}). The syntax
+is:
+
+@smallexample
+@code{OPEN(..., READONLY)}
+@end smallexample
+
+@item SHARE
+The @code{SHARE} specifier allows system-level locking on a unit upon opening
+it for controlled access from multiple processes/threads. The @code{SHARE}
+specifier has several forms:
+
+@smallexample
+OPEN(..., SHARE=sh)
+OPEN(..., SHARED)
+OPEN(..., NOSHARED)
+@end smallexample
+
+Where @emph{sh} in the first form is a character expression that evaluates to
+a value as seen in the table below. The latter two forms are aliases
+for particular values of @emph{sh}:
+
+@multitable @columnfractions .3 .3 .4
+@headitem Explicit form @tab Short form @tab Meaning
+@item @code{SHARE='DENYRW'} @tab @code{NOSHARED} @tab Exclusive (write) lock
+@item @code{SHARE='DENYNONE'} @tab @code{SHARED} @tab Shared (read) lock
+@end multitable
+
+In general only one process may hold an exclusive (write) lock for a given file
+at a time, whereas many processes may hold shared (read) locks for the same
+file.
+
+The behavior of locking may vary with your operating system. On POSIX systems,
+locking is implemented with @code{fcntl}. Consult your corresponding operating
+system's manual pages for further details. Locking via @code{SHARE=} is not
+supported on other systems.
+
+@end table
+
+@node Legacy PARAMETER statements
+@subsection Legacy PARAMETER statements
+@cindex PARAMETER
+
+For compatibility, GNU Fortran supports legacy PARAMETER statements without
+parentheses with @option{-std=legacy}. A warning is emitted if used with
+@option{-std=gnu}, and an error is acknowledged with a real Fortran standard
+flag (@option{-std=f95}, etc...). These statements take the following form:
+
+@smallexample
+implicit real (E)
+parameter e = 2.718282
+real c
+parameter c = 3.0e8
+@end smallexample
+
+@node Default exponents
+@subsection Default exponents
+@cindex exponent
+
+For compatibility, GNU Fortran supports a default exponent of zero in real
+constants with @option{-fdec}. For example, @code{9e} would be
+interpreted as @code{9e0}, rather than an error.
+
+
+@node Extensions not implemented in GNU Fortran
+@section Extensions not implemented in GNU Fortran
+@cindex extensions, not implemented
+
+The long history of the Fortran language, its wide use and broad
+userbase, the large number of different compiler vendors and the lack of
+some features crucial to users in the first standards have lead to the
+existence of a number of important extensions to the language. While
+some of the most useful or popular extensions are supported by the GNU
+Fortran compiler, not all existing extensions are supported. This section
+aims at listing these extensions and offering advice on how best make
+code that uses them running with the GNU Fortran compiler.
+
+@c More can be found here:
+@c -- https://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/Missing-Features.html
+@c -- the list of Fortran and libgfortran bugs closed as WONTFIX:
+@c http://tinyurl.com/2u4h5y
+
+@menu
+* ENCODE and DECODE statements::
+* Variable FORMAT expressions::
+@c * TYPE and ACCEPT I/O Statements::
+@c * DEFAULTFILE, DISPOSE and RECORDTYPE I/O specifiers::
+@c * Omitted arguments in procedure call::
+* Alternate complex function syntax::
+* Volatile COMMON blocks::
+* OPEN( ... NAME=)::
+* Q edit descriptor::
+@end menu
+
+@node ENCODE and DECODE statements
+@subsection @code{ENCODE} and @code{DECODE} statements
+@cindex @code{ENCODE}
+@cindex @code{DECODE}
+
+GNU Fortran does not support the @code{ENCODE} and @code{DECODE}
+statements. These statements are best replaced by @code{READ} and
+@code{WRITE} statements involving internal files (@code{CHARACTER}
+variables and arrays), which have been part of the Fortran standard since
+Fortran 77. For example, replace a code fragment like
+
+@smallexample
+ INTEGER*1 LINE(80)
+ REAL A, B, C
+c ... Code that sets LINE
+ DECODE (80, 9000, LINE) A, B, C
+ 9000 FORMAT (1X, 3(F10.5))
+@end smallexample
+
+@noindent
+with the following:
+
+@smallexample
+ CHARACTER(LEN=80) LINE
+ REAL A, B, C
+c ... Code that sets LINE
+ READ (UNIT=LINE, FMT=9000) A, B, C
+ 9000 FORMAT (1X, 3(F10.5))
+@end smallexample
+
+Similarly, replace a code fragment like
+
+@smallexample
+ INTEGER*1 LINE(80)
+ REAL A, B, C
+c ... Code that sets A, B and C
+ ENCODE (80, 9000, LINE) A, B, C
+ 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))
+@end smallexample
+
+@noindent
+with the following:
+
+@smallexample
+ CHARACTER(LEN=80) LINE
+ REAL A, B, C
+c ... Code that sets A, B and C
+ WRITE (UNIT=LINE, FMT=9000) A, B, C
+ 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))
+@end smallexample
+
+
+@node Variable FORMAT expressions
+@subsection Variable @code{FORMAT} expressions
+@cindex @code{FORMAT}
+
+A variable @code{FORMAT} expression is format statement which includes
+angle brackets enclosing a Fortran expression: @code{FORMAT(I<N>)}. GNU
+Fortran does not support this legacy extension. The effect of variable
+format expressions can be reproduced by using the more powerful (and
+standard) combination of internal output and string formats. For example,
+replace a code fragment like this:
+
+@smallexample
+ WRITE(6,20) INT1
+ 20 FORMAT(I<N+1>)
+@end smallexample
+
+@noindent
+with the following:
+
+@smallexample
+c Variable declaration
+ CHARACTER(LEN=20) FMT
+c
+c Other code here...
+c
+ WRITE(FMT,'("(I", I0, ")")') N+1
+ WRITE(6,FMT) INT1
+@end smallexample
+
+@noindent
+or with:
+
+@smallexample
+c Variable declaration
+ CHARACTER(LEN=20) FMT
+c
+c Other code here...
+c
+ WRITE(FMT,*) N+1
+ WRITE(6,"(I" // ADJUSTL(FMT) // ")") INT1
+@end smallexample
+
+
+@node Alternate complex function syntax
+@subsection Alternate complex function syntax
+@cindex Complex function
+
+Some Fortran compilers, including @command{g77}, let the user declare
+complex functions with the syntax @code{COMPLEX FUNCTION name*16()}, as
+well as @code{COMPLEX*16 FUNCTION name()}. Both are non-standard, legacy
+extensions. @command{gfortran} accepts the latter form, which is more
+common, but not the former.
+
+
+@node Volatile COMMON blocks
+@subsection Volatile @code{COMMON} blocks
+@cindex @code{VOLATILE}
+@cindex @code{COMMON}
+
+Some Fortran compilers, including @command{g77}, let the user declare
+@code{COMMON} with the @code{VOLATILE} attribute. This is
+invalid standard Fortran syntax and is not supported by
+@command{gfortran}. Note that @command{gfortran} accepts
+@code{VOLATILE} variables in @code{COMMON} blocks since revision 4.3.
+
+
+@node OPEN( ... NAME=)
+@subsection @code{OPEN( ... NAME=)}
+@cindex @code{NAME}
+
+Some Fortran compilers, including @command{g77}, let the user declare
+@code{OPEN( ... NAME=)}. This is
+invalid standard Fortran syntax and is not supported by
+@command{gfortran}. @code{OPEN( ... NAME=)} should be replaced
+with @code{OPEN( ... FILE=)}.
+
+@node Q edit descriptor
+@subsection @code{Q} edit descriptor
+@cindex @code{Q} edit descriptor
+
+Some Fortran compilers provide the @code{Q} edit descriptor, which
+transfers the number of characters left within an input record into an
+integer variable.
+
+A direct replacement of the @code{Q} edit descriptor is not available
+in @command{gfortran}. How to replicate its functionality using
+standard-conforming code depends on what the intent of the original
+code is.
+
+Options to replace @code{Q} may be to read the whole line into a
+character variable and then counting the number of non-blank
+characters left using @code{LEN_TRIM}. Another method may be to use
+formatted stream, read the data up to the position where the @code{Q}
+descriptor occurred, use @code{INQUIRE} to get the file position,
+count the characters up to the next @code{NEW_LINE} and then start
+reading from the position marked previously.
+
+
+@c ---------------------------------------------------------------------
+@c ---------------------------------------------------------------------
+@c Mixed-Language Programming
+@c ---------------------------------------------------------------------
+
+@node Mixed-Language Programming
+@chapter Mixed-Language Programming
+@cindex Interoperability
+@cindex Mixed-language programming
+
+@menu
+* Interoperability with C::
+* GNU Fortran Compiler Directives::
+* Non-Fortran Main Program::
+* Naming and argument-passing conventions::
+@end menu
+
+This chapter is about mixed-language interoperability, but also applies
+if one links Fortran code compiled by different compilers. In most cases,
+use of the C Binding features of the Fortran 2003 standard is sufficient,
+and their use is highly recommended.
+
+
+@node Interoperability with C
+@section Interoperability with C
+
+@menu
+* Intrinsic Types::
+* Derived Types and struct::
+* Interoperable Global Variables::
+* Interoperable Subroutines and Functions::
+* Working with Pointers::
+* Further Interoperability of Fortran with C::
+@end menu
+
+Since Fortran 2003 (ISO/IEC 1539-1:2004(E)) there is a
+standardized way to generate procedure and derived-type
+declarations and global variables which are interoperable with C
+(ISO/IEC 9899:1999). The @code{bind(C)} attribute has been added
+to inform the compiler that a symbol shall be interoperable with C;
+also, some constraints are added. Note, however, that not
+all C features have a Fortran equivalent or vice versa. For instance,
+neither C's unsigned integers nor C's functions with variable number
+of arguments have an equivalent in Fortran.
+
+Note that array dimensions are reversely ordered in C and that arrays in
+C always start with index 0 while in Fortran they start by default with
+1. Thus, an array declaration @code{A(n,m)} in Fortran matches
+@code{A[m][n]} in C and accessing the element @code{A(i,j)} matches
+@code{A[j-1][i-1]}. The element following @code{A(i,j)} (C: @code{A[j-1][i-1]};
+assuming @math{i < n}) in memory is @code{A(i+1,j)} (C: @code{A[j-1][i]}).
+
+@node Intrinsic Types
+@subsection Intrinsic Types
+
+In order to ensure that exactly the same variable type and kind is used
+in C and Fortran, the named constants shall be used which are defined in the
+@code{ISO_C_BINDING} intrinsic module. That module contains named constants
+for kind parameters and character named constants for the escape sequences
+in C. For a list of the constants, see @ref{ISO_C_BINDING}.
+
+For logical types, please note that the Fortran standard only guarantees
+interoperability between C99's @code{_Bool} and Fortran's @code{C_Bool}-kind
+logicals and C99 defines that @code{true} has the value 1 and @code{false}
+the value 0. Using any other integer value with GNU Fortran's @code{LOGICAL}
+(with any kind parameter) gives an undefined result. (Passing other integer
+values than 0 and 1 to GCC's @code{_Bool} is also undefined, unless the
+integer is explicitly or implicitly casted to @code{_Bool}.)
+
+
+
+@node Derived Types and struct
+@subsection Derived Types and struct
+
+For compatibility of derived types with @code{struct}, one needs to use
+the @code{BIND(C)} attribute in the type declaration. For instance, the
+following type declaration
+
+@smallexample
+ USE ISO_C_BINDING
+ TYPE, BIND(C) :: myType
+ INTEGER(C_INT) :: i1, i2
+ INTEGER(C_SIGNED_CHAR) :: i3
+ REAL(C_DOUBLE) :: d1
+ COMPLEX(C_FLOAT_COMPLEX) :: c1
+ CHARACTER(KIND=C_CHAR) :: str(5)
+ END TYPE
+@end smallexample
+
+matches the following @code{struct} declaration in C
+
+@smallexample
+ struct @{
+ int i1, i2;
+ /* Note: "char" might be signed or unsigned. */
+ signed char i3;
+ double d1;
+ float _Complex c1;
+ char str[5];
+ @} myType;
+@end smallexample
+
+Derived types with the C binding attribute shall not have the @code{sequence}
+attribute, type parameters, the @code{extends} attribute, nor type-bound
+procedures. Every component must be of interoperable type and kind and may not
+have the @code{pointer} or @code{allocatable} attribute. The names of the
+components are irrelevant for interoperability.
+
+As there exist no direct Fortran equivalents, neither unions nor structs
+with bit field or variable-length array members are interoperable.
+
+@node Interoperable Global Variables
+@subsection Interoperable Global Variables
+
+Variables can be made accessible from C using the C binding attribute,
+optionally together with specifying a binding name. Those variables
+have to be declared in the declaration part of a @code{MODULE},
+be of interoperable type, and have neither the @code{pointer} nor
+the @code{allocatable} attribute.
+
+@smallexample
+ MODULE m
+ USE myType_module
+ USE ISO_C_BINDING
+ integer(C_INT), bind(C, name="_MyProject_flags") :: global_flag
+ type(myType), bind(C) :: tp
+ END MODULE
+@end smallexample
+
+Here, @code{_MyProject_flags} is the case-sensitive name of the variable
+as seen from C programs while @code{global_flag} is the case-insensitive
+name as seen from Fortran. If no binding name is specified, as for
+@var{tp}, the C binding name is the (lowercase) Fortran binding name.
+If a binding name is specified, only a single variable may be after the
+double colon. Note of warning: You cannot use a global variable to
+access @var{errno} of the C library as the C standard allows it to be
+a macro. Use the @code{IERRNO} intrinsic (GNU extension) instead.
+
+@node Interoperable Subroutines and Functions
+@subsection Interoperable Subroutines and Functions
+
+Subroutines and functions have to have the @code{BIND(C)} attribute to
+be compatible with C. The dummy argument declaration is relatively
+straightforward. However, one needs to be careful because C uses
+call-by-value by default while Fortran behaves usually similar to
+call-by-reference. Furthermore, strings and pointers are handled
+differently. Note that in Fortran 2003 and 2008 only explicit size
+and assumed-size arrays are supported but not assumed-shape or
+deferred-shape (i.e. allocatable or pointer) arrays. However, those
+are allowed since the Technical Specification 29113, see
+@ref{Further Interoperability of Fortran with C}
+
+To pass a variable by value, use the @code{VALUE} attribute.
+Thus, the following C prototype
+
+@smallexample
+@code{int func(int i, int *j)}
+@end smallexample
+
+matches the Fortran declaration
+
+@smallexample
+ integer(c_int) function func(i,j)
+ use iso_c_binding, only: c_int
+ integer(c_int), VALUE :: i
+ integer(c_int) :: j
+@end smallexample
+
+Note that pointer arguments also frequently need the @code{VALUE} attribute,
+see @ref{Working with Pointers}.
+
+Strings are handled quite differently in C and Fortran. In C a string
+is a @code{NUL}-terminated array of characters while in Fortran each string
+has a length associated with it and is thus not terminated (by e.g.
+@code{NUL}). For example, if one wants to use the following C function,
+
+@smallexample
+ #include <stdio.h>
+ void print_C(char *string) /* equivalent: char string[] */
+ @{
+ printf("%s\n", string);
+ @}
+@end smallexample
+
+to print ``Hello World'' from Fortran, one can call it using
+
+@smallexample
+ use iso_c_binding, only: C_CHAR, C_NULL_CHAR
+ interface
+ subroutine print_c(string) bind(C, name="print_C")
+ use iso_c_binding, only: c_char
+ character(kind=c_char) :: string(*)
+ end subroutine print_c
+ end interface
+ call print_c(C_CHAR_"Hello World"//C_NULL_CHAR)
+@end smallexample
+
+As the example shows, one needs to ensure that the
+string is @code{NUL} terminated. Additionally, the dummy argument
+@var{string} of @code{print_C} is a length-one assumed-size
+array; using @code{character(len=*)} is not allowed. The example
+above uses @code{c_char_"Hello World"} to ensure the string
+literal has the right type; typically the default character
+kind and @code{c_char} are the same and thus @code{"Hello World"}
+is equivalent. However, the standard does not guarantee this.
+
+The use of strings is now further illustrated using the C library
+function @code{strncpy}, whose prototype is
+
+@smallexample
+ char *strncpy(char *restrict s1, const char *restrict s2, size_t n);
+@end smallexample
+
+The function @code{strncpy} copies at most @var{n} characters from
+string @var{s2} to @var{s1} and returns @var{s1}. In the following
+example, we ignore the return value:
+
+@smallexample
+ use iso_c_binding
+ implicit none
+ character(len=30) :: str,str2
+ interface
+ ! Ignore the return value of strncpy -> subroutine
+ ! "restrict" is always assumed if we do not pass a pointer
+ subroutine strncpy(dest, src, n) bind(C)
+ import
+ character(kind=c_char), intent(out) :: dest(*)
+ character(kind=c_char), intent(in) :: src(*)
+ integer(c_size_t), value, intent(in) :: n
+ end subroutine strncpy
+ end interface
+ str = repeat('X',30) ! Initialize whole string with 'X'
+ call strncpy(str, c_char_"Hello World"//C_NULL_CHAR, &
+ len(c_char_"Hello World",kind=c_size_t))
+ print '(a)', str ! prints: "Hello WorldXXXXXXXXXXXXXXXXXXX"
+ end
+@end smallexample
+
+The intrinsic procedures are described in @ref{Intrinsic Procedures}.
+
+@node Working with Pointers
+@subsection Working with Pointers
+
+C pointers are represented in Fortran via the special opaque derived type
+@code{type(c_ptr)} (with private components). Thus one needs to
+use intrinsic conversion procedures to convert from or to C pointers.
+
+For some applications, using an assumed type (@code{TYPE(*)}) can be an
+alternative to a C pointer; see
+@ref{Further Interoperability of Fortran with C}.
+
+For example,
+
+@smallexample
+ use iso_c_binding
+ type(c_ptr) :: cptr1, cptr2
+ integer, target :: array(7), scalar
+ integer, pointer :: pa(:), ps
+ cptr1 = c_loc(array(1)) ! The programmer needs to ensure that the
+ ! array is contiguous if required by the C
+ ! procedure
+ cptr2 = c_loc(scalar)
+ call c_f_pointer(cptr2, ps)
+ call c_f_pointer(cptr2, pa, shape=[7])
+@end smallexample
+
+When converting C to Fortran arrays, the one-dimensional @code{SHAPE} argument
+has to be passed.
+
+If a pointer is a dummy-argument of an interoperable procedure, it usually
+has to be declared using the @code{VALUE} attribute. @code{void*}
+matches @code{TYPE(C_PTR), VALUE}, while @code{TYPE(C_PTR)} alone
+matches @code{void**}.
+
+Procedure pointers are handled analogously to pointers; the C type is
+@code{TYPE(C_FUNPTR)} and the intrinsic conversion procedures are
+@code{C_F_PROCPOINTER} and @code{C_FUNLOC}.
+
+Let us consider two examples of actually passing a procedure pointer from
+C to Fortran and vice versa. Note that these examples are also very
+similar to passing ordinary pointers between both languages. First,
+consider this code in C:
+
+@smallexample
+/* Procedure implemented in Fortran. */
+void get_values (void (*)(double));
+
+/* Call-back routine we want called from Fortran. */
+void
+print_it (double x)
+@{
+ printf ("Number is %f.\n", x);
+@}
+
+/* Call Fortran routine and pass call-back to it. */
+void
+foobar ()
+@{
+ get_values (&print_it);
+@}
+@end smallexample
+
+A matching implementation for @code{get_values} in Fortran, that correctly
+receives the procedure pointer from C and is able to call it, is given
+in the following @code{MODULE}:
+
+@smallexample
+MODULE m
+ IMPLICIT NONE
+
+ ! Define interface of call-back routine.
+ ABSTRACT INTERFACE
+ SUBROUTINE callback (x)
+ USE, INTRINSIC :: ISO_C_BINDING
+ REAL(KIND=C_DOUBLE), INTENT(IN), VALUE :: x
+ END SUBROUTINE callback
+ END INTERFACE
+
+CONTAINS
+
+ ! Define C-bound procedure.
+ SUBROUTINE get_values (cproc) BIND(C)
+ USE, INTRINSIC :: ISO_C_BINDING
+ TYPE(C_FUNPTR), INTENT(IN), VALUE :: cproc
+
+ PROCEDURE(callback), POINTER :: proc
+
+ ! Convert C to Fortran procedure pointer.
+ CALL C_F_PROCPOINTER (cproc, proc)
+
+ ! Call it.
+ CALL proc (1.0_C_DOUBLE)
+ CALL proc (-42.0_C_DOUBLE)
+ CALL proc (18.12_C_DOUBLE)
+ END SUBROUTINE get_values
+
+END MODULE m
+@end smallexample
+
+Next, we want to call a C routine that expects a procedure pointer argument
+and pass it a Fortran procedure (which clearly must be interoperable!).
+Again, the C function may be:
+
+@smallexample
+int
+call_it (int (*func)(int), int arg)
+@{
+ return func (arg);
+@}
+@end smallexample
+
+It can be used as in the following Fortran code:
+
+@smallexample
+MODULE m
+ USE, INTRINSIC :: ISO_C_BINDING
+ IMPLICIT NONE
+
+ ! Define interface of C function.
+ INTERFACE
+ INTEGER(KIND=C_INT) FUNCTION call_it (func, arg) BIND(C)
+ USE, INTRINSIC :: ISO_C_BINDING
+ TYPE(C_FUNPTR), INTENT(IN), VALUE :: func
+ INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg
+ END FUNCTION call_it
+ END INTERFACE
+
+CONTAINS
+
+ ! Define procedure passed to C function.
+ ! It must be interoperable!
+ INTEGER(KIND=C_INT) FUNCTION double_it (arg) BIND(C)
+ INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg
+ double_it = arg + arg
+ END FUNCTION double_it
+
+ ! Call C function.
+ SUBROUTINE foobar ()
+ TYPE(C_FUNPTR) :: cproc
+ INTEGER(KIND=C_INT) :: i
+
+ ! Get C procedure pointer.
+ cproc = C_FUNLOC (double_it)
+
+ ! Use it.
+ DO i = 1_C_INT, 10_C_INT
+ PRINT *, call_it (cproc, i)
+ END DO
+ END SUBROUTINE foobar
+
+END MODULE m
+@end smallexample
+
+@node Further Interoperability of Fortran with C
+@subsection Further Interoperability of Fortran with C
+
+The Technical Specification ISO/IEC TS 29113:2012 on further
+interoperability of Fortran with C extends the interoperability support
+of Fortran 2003 and Fortran 2008. Besides removing some restrictions
+and constraints, it adds assumed-type (@code{TYPE(*)}) and assumed-rank
+(@code{dimension}) variables and allows for interoperability of
+assumed-shape, assumed-rank and deferred-shape arrays, including
+allocatables and pointers.
+
+Note: Currently, GNU Fortran does not use internally the array descriptor
+(dope vector) as specified in the Technical Specification, but uses
+an array descriptor with different fields. Assumed type and assumed rank
+formal arguments are converted in the library to the specified form. The
+ISO_Fortran_binding API functions (also Fortran 2018 18.4) are implemented
+in libgfortran. Alternatively, the Chasm Language Interoperability Tools,
+@url{http://chasm-interop.sourceforge.net/}, provide an interface to GNU
+Fortran's array descriptor.
+
+The Technical Specification adds the following new features, which
+are supported by GNU Fortran:
+
+@itemize @bullet
+
+@item The @code{ASYNCHRONOUS} attribute has been clarified and
+extended to allow its use with asynchronous communication in
+user-provided libraries such as in implementations of the
+Message Passing Interface specification.
+
+@item Many constraints have been relaxed, in particular for
+the @code{C_LOC} and @code{C_F_POINTER} intrinsics.
+
+@item The @code{OPTIONAL} attribute is now allowed for dummy
+arguments; an absent argument matches a @code{NULL} pointer.
+
+@item Assumed types (@code{TYPE(*)}) have been added, which may
+only be used for dummy arguments. They are unlimited polymorphic
+but contrary to @code{CLASS(*)} they do not contain any type
+information, similar to C's @code{void *} pointers. Expressions
+of any type and kind can be passed; thus, it can be used as
+replacement for @code{TYPE(C_PTR)}, avoiding the use of
+@code{C_LOC} in the caller.
+
+Note, however, that @code{TYPE(*)} only accepts scalar arguments,
+unless the @code{DIMENSION} is explicitly specified. As
+@code{DIMENSION(*)} only supports array (including array elements) but
+no scalars, it is not a full replacement for @code{C_LOC}. On the
+other hand, assumed-type assumed-rank dummy arguments
+(@code{TYPE(*), DIMENSION(..)}) allow for both scalars and arrays, but
+require special code on the callee side to handle the array descriptor.
+
+@item Assumed-rank arrays (@code{DIMENSION(..)}) as dummy argument
+allow that scalars and arrays of any rank can be passed as actual
+argument. As the Technical Specification does not provide for direct
+means to operate with them, they have to be used either from the C side
+or be converted using @code{C_LOC} and @code{C_F_POINTER} to scalars
+or arrays of a specific rank. The rank can be determined using the
+@code{RANK} intrinisic.
+@end itemize
+
+
+Currently unimplemented:
+
+@itemize @bullet
+
+@item GNU Fortran always uses an array descriptor, which does not
+match the one of the Technical Specification. The
+@code{ISO_Fortran_binding.h} header file and the C functions it
+specifies are not available.
+
+@item Using assumed-shape, assumed-rank and deferred-shape arrays in
+@code{BIND(C)} procedures is not fully supported. In particular,
+C interoperable strings of other length than one are not supported
+as this requires the new array descriptor.
+@end itemize
+
+
+@node GNU Fortran Compiler Directives
+@section GNU Fortran Compiler Directives
+
+@menu
+* ATTRIBUTES directive::
+* UNROLL directive::
+* BUILTIN directive::
+* IVDEP directive::
+* VECTOR directive::
+* NOVECTOR directive::
+@end menu
+
+@node ATTRIBUTES directive
+@subsection ATTRIBUTES directive
+
+The Fortran standard describes how a conforming program shall
+behave; however, the exact implementation is not standardized. In order
+to allow the user to choose specific implementation details, compiler
+directives can be used to set attributes of variables and procedures
+which are not part of the standard. Whether a given attribute is
+supported and its exact effects depend on both the operating system and
+on the processor; see
+@ref{Top,,C Extensions,gcc,Using the GNU Compiler Collection (GCC)}
+for details.
+
+For procedures and procedure pointers, the following attributes can
+be used to change the calling convention:
+
+@itemize
+@item @code{CDECL} -- standard C calling convention
+@item @code{STDCALL} -- convention where the called procedure pops the stack
+@item @code{FASTCALL} -- part of the arguments are passed via registers
+instead using the stack
+@end itemize
+
+Besides changing the calling convention, the attributes also influence
+the decoration of the symbol name, e.g., by a leading underscore or by
+a trailing at-sign followed by the number of bytes on the stack. When
+assigning a procedure to a procedure pointer, both should use the same
+calling convention.
+
+On some systems, procedures and global variables (module variables and
+@code{COMMON} blocks) need special handling to be accessible when they
+are in a shared library. The following attributes are available:
+
+@itemize
+@item @code{DLLEXPORT} -- provide a global pointer to a pointer in the DLL
+@item @code{DLLIMPORT} -- reference the function or variable using a
+global pointer
+@end itemize
+
+For dummy arguments, the @code{NO_ARG_CHECK} attribute can be used; in
+other compilers, it is also known as @code{IGNORE_TKR}. For dummy arguments
+with this attribute actual arguments of any type and kind (similar to
+@code{TYPE(*)}), scalars and arrays of any rank (no equivalent
+in Fortran standard) are accepted. As with @code{TYPE(*)}, the argument
+is unlimited polymorphic and no type information is available.
+Additionally, the argument may only be passed to dummy arguments
+with the @code{NO_ARG_CHECK} attribute and as argument to the
+@code{PRESENT} intrinsic function and to @code{C_LOC} of the
+@code{ISO_C_BINDING} module.
+
+Variables with @code{NO_ARG_CHECK} attribute shall be of assumed-type
+(@code{TYPE(*)}; recommended) or of type @code{INTEGER}, @code{LOGICAL},
+@code{REAL} or @code{COMPLEX}. They shall not have the @code{ALLOCATE},
+@code{CODIMENSION}, @code{INTENT(OUT)}, @code{POINTER} or @code{VALUE}
+attribute; furthermore, they shall be either scalar or of assumed-size
+(@code{dimension(*)}). As @code{TYPE(*)}, the @code{NO_ARG_CHECK} attribute
+requires an explicit interface.
+
+@itemize
+@item @code{NO_ARG_CHECK} -- disable the type, kind and rank checking
+@item @code{DEPRECATED} -- print a warning when using a such-tagged
+deprecated procedure, variable or parameter; the warning can be suppressed
+with @option{-Wno-deprecated-declarations}.
+@end itemize
+
+
+The attributes are specified using the syntax
+
+@code{!GCC$ ATTRIBUTES} @var{attribute-list} @code{::} @var{variable-list}
+
+where in free-form source code only whitespace is allowed before @code{!GCC$}
+and in fixed-form source code @code{!GCC$}, @code{cGCC$} or @code{*GCC$} shall
+start in the first column.
+
+For procedures, the compiler directives shall be placed into the body
+of the procedure; for variables and procedure pointers, they shall be in
+the same declaration part as the variable or procedure pointer.
+
+
+@node UNROLL directive
+@subsection UNROLL directive
+
+The syntax of the directive is
+
+@code{!GCC$ unroll N}
+
+You can use this directive to control how many times a loop should be unrolled.
+It must be placed immediately before a @code{DO} loop and applies only to the
+loop that follows. N is an integer constant specifying the unrolling factor.
+The values of 0 and 1 block any unrolling of the loop.
+
+
+@node BUILTIN directive
+@subsection BUILTIN directive
+
+The syntax of the directive is
+
+@code{!GCC$ BUILTIN (B) attributes simd FLAGS IF('target')}
+
+You can use this directive to define which middle-end built-ins provide vector
+implementations. @code{B} is name of the middle-end built-in. @code{FLAGS}
+are optional and must be either "(inbranch)" or "(notinbranch)".
+@code{IF} statement is optional and is used to filter multilib ABIs
+for the built-in that should be vectorized. Example usage:
+
+@smallexample
+!GCC$ builtin (sinf) attributes simd (notinbranch) if('x86_64')
+@end smallexample
+
+The purpose of the directive is to provide an API among the GCC compiler and
+the GNU C Library which would define vector implementations of math routines.
+
+
+@node IVDEP directive
+@subsection IVDEP directive
+
+The syntax of the directive is
+
+@code{!GCC$ ivdep}
+
+This directive tells the compiler to ignore vector dependencies in the
+following loop. It must be placed immediately before a @code{DO} loop
+and applies only to the loop that follows.
+
+Sometimes the compiler may not have sufficient information to decide
+whether a particular loop is vectorizable due to potential
+dependencies between iterations. The purpose of the directive is to
+tell the compiler that vectorization is safe.
+
+This directive is intended for annotation of existing code. For new
+code it is recommended to consider OpenMP SIMD directives as potential
+alternative.
+
+
+@node VECTOR directive
+@subsection VECTOR directive
+
+The syntax of the directive is
+
+@code{!GCC$ vector}
+
+This directive tells the compiler to vectorize the following loop. It
+must be placed immediately before a @code{DO} loop and applies only to
+the loop that follows.
+
+
+@node NOVECTOR directive
+@subsection NOVECTOR directive
+
+The syntax of the directive is
+
+@code{!GCC$ novector}
+
+This directive tells the compiler to not vectorize the following loop.
+It must be placed immediately before a @code{DO} loop and applies only
+to the loop that follows.
+
+
+@node Non-Fortran Main Program
+@section Non-Fortran Main Program
+
+@menu
+* _gfortran_set_args:: Save command-line arguments
+* _gfortran_set_options:: Set library option flags
+* _gfortran_set_convert:: Set endian conversion
+* _gfortran_set_record_marker:: Set length of record markers
+* _gfortran_set_fpe:: Set when a Floating Point Exception should be raised
+* _gfortran_set_max_subrecord_length:: Set subrecord length
+@end menu
+
+Even if you are doing mixed-language programming, it is very
+likely that you do not need to know or use the information in this
+section. Since it is about the internal structure of GNU Fortran,
+it may also change in GCC minor releases.
+
+When you compile a @code{PROGRAM} with GNU Fortran, a function
+with the name @code{main} (in the symbol table of the object file)
+is generated, which initializes the libgfortran library and then
+calls the actual program which uses the name @code{MAIN__}, for
+historic reasons. If you link GNU Fortran compiled procedures
+to, e.g., a C or C++ program or to a Fortran program compiled by
+a different compiler, the libgfortran library is not initialized
+and thus a few intrinsic procedures do not work properly, e.g.
+those for obtaining the command-line arguments.
+
+Therefore, if your @code{PROGRAM} is not compiled with
+GNU Fortran and the GNU Fortran compiled procedures require
+intrinsics relying on the library initialization, you need to
+initialize the library yourself. Using the default options,
+gfortran calls @code{_gfortran_set_args} and
+@code{_gfortran_set_options}. The initialization of the former
+is needed if the called procedures access the command line
+(and for backtracing); the latter sets some flags based on the
+standard chosen or to enable backtracing. In typical programs,
+it is not necessary to call any initialization function.
+
+If your @code{PROGRAM} is compiled with GNU Fortran, you shall
+not call any of the following functions. The libgfortran
+initialization functions are shown in C syntax but using C
+bindings they are also accessible from Fortran.
+
+
+@node _gfortran_set_args
+@subsection @code{_gfortran_set_args} --- Save command-line arguments
+@fnindex _gfortran_set_args
+@cindex libgfortran initialization, set_args
+
+@table @asis
+@item @emph{Description}:
+@code{_gfortran_set_args} saves the command-line arguments; this
+initialization is required if any of the command-line intrinsics
+is called. Additionally, it shall be called if backtracing is
+enabled (see @code{_gfortran_set_options}).
+
+@item @emph{Syntax}:
+@code{void _gfortran_set_args (int argc, char *argv[])}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{argc} @tab number of command line argument strings
+@item @var{argv} @tab the command-line argument strings; argv[0]
+is the pathname of the executable itself.
+@end multitable
+
+@item @emph{Example}:
+@smallexample
+int main (int argc, char *argv[])
+@{
+ /* Initialize libgfortran. */
+ _gfortran_set_args (argc, argv);
+ return 0;
+@}
+@end smallexample
+@end table
+
+
+@node _gfortran_set_options
+@subsection @code{_gfortran_set_options} --- Set library option flags
+@fnindex _gfortran_set_options
+@cindex libgfortran initialization, set_options
+
+@table @asis
+@item @emph{Description}:
+@code{_gfortran_set_options} sets several flags related to the Fortran
+standard to be used, whether backtracing should be enabled
+and whether range checks should be performed. The syntax allows for
+upward compatibility since the number of passed flags is specified; for
+non-passed flags, the default value is used. See also
+@pxref{Code Gen Options}. Please note that not all flags are actually
+used.
+
+@item @emph{Syntax}:
+@code{void _gfortran_set_options (int num, int options[])}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{num} @tab number of options passed
+@item @var{argv} @tab The list of flag values
+@end multitable
+
+@item @emph{option flag list}:
+@multitable @columnfractions .15 .70
+@item @var{option}[0] @tab Allowed standard; can give run-time errors
+if e.g. an input-output edit descriptor is invalid in a given
+standard. Possible values are (bitwise or-ed) @code{GFC_STD_F77} (1),
+@code{GFC_STD_F95_OBS} (2), @code{GFC_STD_F95_DEL} (4),
+@code{GFC_STD_F95} (8), @code{GFC_STD_F2003} (16), @code{GFC_STD_GNU}
+(32), @code{GFC_STD_LEGACY} (64), @code{GFC_STD_F2008} (128),
+@code{GFC_STD_F2008_OBS} (256), @code{GFC_STD_F2008_TS} (512),
+@code{GFC_STD_F2018} (1024), @code{GFC_STD_F2018_OBS} (2048), and
+@code{GFC_STD=F2018_DEL} (4096). Default: @code{GFC_STD_F95_OBS |
+GFC_STD_F95_DEL | GFC_STD_F95 | GFC_STD_F2003 | GFC_STD_F2008 |
+GFC_STD_F2008_TS | GFC_STD_F2008_OBS | GFC_STD_F77 | GFC_STD_F2018 |
+GFC_STD_F2018_OBS | GFC_STD_F2018_DEL | GFC_STD_GNU | GFC_STD_LEGACY}.
+@item @var{option}[1] @tab Standard-warning flag; prints a warning to
+standard error. Default: @code{GFC_STD_F95_DEL | GFC_STD_LEGACY}.
+@item @var{option}[2] @tab If non zero, enable pedantic checking.
+Default: off.
+@item @var{option}[3] @tab Unused.
+@item @var{option}[4] @tab If non zero, enable backtracing on run-time
+errors. Default: off. (Default in the compiler: on.)
+Note: Installs a signal handler and requires command-line
+initialization using @code{_gfortran_set_args}.
+@item @var{option}[5] @tab If non zero, supports signed zeros.
+Default: enabled.
+@item @var{option}[6] @tab Enables run-time checking. Possible values
+are (bitwise or-ed): GFC_RTCHECK_BOUNDS (1), GFC_RTCHECK_ARRAY_TEMPS (2),
+GFC_RTCHECK_RECURSION (4), GFC_RTCHECK_DO (8), GFC_RTCHECK_POINTER (16),
+GFC_RTCHECK_MEM (32), GFC_RTCHECK_BITS (64).
+Default: disabled.
+@item @var{option}[7] @tab Unused.
+@item @var{option}[8] @tab Show a warning when invoking @code{STOP} and
+@code{ERROR STOP} if a floating-point exception occurred. Possible values
+are (bitwise or-ed) @code{GFC_FPE_INVALID} (1), @code{GFC_FPE_DENORMAL} (2),
+@code{GFC_FPE_ZERO} (4), @code{GFC_FPE_OVERFLOW} (8),
+@code{GFC_FPE_UNDERFLOW} (16), @code{GFC_FPE_INEXACT} (32). Default: None (0).
+(Default in the compiler: @code{GFC_FPE_INVALID | GFC_FPE_DENORMAL |
+GFC_FPE_ZERO | GFC_FPE_OVERFLOW | GFC_FPE_UNDERFLOW}.)
+@end multitable
+
+@item @emph{Example}:
+@smallexample
+ /* Use gfortran 4.9 default options. */
+ static int options[] = @{68, 511, 0, 0, 1, 1, 0, 0, 31@};
+ _gfortran_set_options (9, &options);
+@end smallexample
+@end table
+
+
+@node _gfortran_set_convert
+@subsection @code{_gfortran_set_convert} --- Set endian conversion
+@fnindex _gfortran_set_convert
+@cindex libgfortran initialization, set_convert
+
+@table @asis
+@item @emph{Description}:
+@code{_gfortran_set_convert} set the representation of data for
+unformatted files.
+
+@item @emph{Syntax}:
+@code{void _gfortran_set_convert (int conv)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{conv} @tab Endian conversion, possible values:
+GFC_CONVERT_NATIVE (0, default), GFC_CONVERT_SWAP (1),
+GFC_CONVERT_BIG (2), GFC_CONVERT_LITTLE (3).
+@end multitable
+
+@item @emph{Example}:
+@smallexample
+int main (int argc, char *argv[])
+@{
+ /* Initialize libgfortran. */
+ _gfortran_set_args (argc, argv);
+ _gfortran_set_convert (1);
+ return 0;
+@}
+@end smallexample
+@end table
+
+
+@node _gfortran_set_record_marker
+@subsection @code{_gfortran_set_record_marker} --- Set length of record markers
+@fnindex _gfortran_set_record_marker
+@cindex libgfortran initialization, set_record_marker
+
+@table @asis
+@item @emph{Description}:
+@code{_gfortran_set_record_marker} sets the length of record markers
+for unformatted files.
+
+@item @emph{Syntax}:
+@code{void _gfortran_set_record_marker (int val)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{val} @tab Length of the record marker; valid values
+are 4 and 8. Default is 4.
+@end multitable
+
+@item @emph{Example}:
+@smallexample
+int main (int argc, char *argv[])
+@{
+ /* Initialize libgfortran. */
+ _gfortran_set_args (argc, argv);
+ _gfortran_set_record_marker (8);
+ return 0;
+@}
+@end smallexample
+@end table
+
+
+@node _gfortran_set_fpe
+@subsection @code{_gfortran_set_fpe} --- Enable floating point exception traps
+@fnindex _gfortran_set_fpe
+@cindex libgfortran initialization, set_fpe
+
+@table @asis
+@item @emph{Description}:
+@code{_gfortran_set_fpe} enables floating point exception traps for
+the specified exceptions. On most systems, this will result in a
+SIGFPE signal being sent and the program being aborted.
+
+@item @emph{Syntax}:
+@code{void _gfortran_set_fpe (int val)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{option}[0] @tab IEEE exceptions. Possible values are
+(bitwise or-ed) zero (0, default) no trapping,
+@code{GFC_FPE_INVALID} (1), @code{GFC_FPE_DENORMAL} (2),
+@code{GFC_FPE_ZERO} (4), @code{GFC_FPE_OVERFLOW} (8),
+@code{GFC_FPE_UNDERFLOW} (16), and @code{GFC_FPE_INEXACT} (32).
+@end multitable
+
+@item @emph{Example}:
+@smallexample
+int main (int argc, char *argv[])
+@{
+ /* Initialize libgfortran. */
+ _gfortran_set_args (argc, argv);
+ /* FPE for invalid operations such as SQRT(-1.0). */
+ _gfortran_set_fpe (1);
+ return 0;
+@}
+@end smallexample
+@end table
+
+
+@node _gfortran_set_max_subrecord_length
+@subsection @code{_gfortran_set_max_subrecord_length} --- Set subrecord length
+@fnindex _gfortran_set_max_subrecord_length
+@cindex libgfortran initialization, set_max_subrecord_length
+
+@table @asis
+@item @emph{Description}:
+@code{_gfortran_set_max_subrecord_length} set the maximum length
+for a subrecord. This option only makes sense for testing and
+debugging of unformatted I/O.
+
+@item @emph{Syntax}:
+@code{void _gfortran_set_max_subrecord_length (int val)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{val} @tab the maximum length for a subrecord;
+the maximum permitted value is 2147483639, which is also
+the default.
+@end multitable
+
+@item @emph{Example}:
+@smallexample
+int main (int argc, char *argv[])
+@{
+ /* Initialize libgfortran. */
+ _gfortran_set_args (argc, argv);
+ _gfortran_set_max_subrecord_length (8);
+ return 0;
+@}
+@end smallexample
+@end table
+
+
+@node Naming and argument-passing conventions
+@section Naming and argument-passing conventions
+
+This section gives an overview about the naming convention of procedures
+and global variables and about the argument passing conventions used by
+GNU Fortran. If a C binding has been specified, the naming convention
+and some of the argument-passing conventions change. If possible,
+mixed-language and mixed-compiler projects should use the better defined
+C binding for interoperability. See @pxref{Interoperability with C}.
+
+@menu
+* Naming conventions::
+* Argument passing conventions::
+@end menu
+
+
+@node Naming conventions
+@subsection Naming conventions
+
+According the Fortran standard, valid Fortran names consist of a letter
+between @code{A} to @code{Z}, @code{a} to @code{z}, digits @code{0},
+@code{1} to @code{9} and underscores (@code{_}) with the restriction
+that names may only start with a letter. As vendor extension, the
+dollar sign (@code{$}) is additionally permitted with the option
+@option{-fdollar-ok}, but not as first character and only if the
+target system supports it.
+
+By default, the procedure name is the lower-cased Fortran name with an
+appended underscore (@code{_}); using @option{-fno-underscoring} no
+underscore is appended while @code{-fsecond-underscore} appends two
+underscores. Depending on the target system and the calling convention,
+the procedure might be additionally dressed; for instance, on 32bit
+Windows with @code{stdcall}, an at-sign @code{@@} followed by an integer
+number is appended. For the changing the calling convention, see
+@pxref{GNU Fortran Compiler Directives}.
+
+For common blocks, the same convention is used, i.e. by default an
+underscore is appended to the lower-cased Fortran name. Blank commons
+have the name @code{__BLNK__}.
+
+For procedures and variables declared in the specification space of a
+module, the name is formed by @code{__}, followed by the lower-cased
+module name, @code{_MOD_}, and the lower-cased Fortran name. Note that
+no underscore is appended.
+
+
+@node Argument passing conventions
+@subsection Argument passing conventions
+
+Subroutines do not return a value (matching C99's @code{void}) while
+functions either return a value as specified in the platform ABI or
+the result variable is passed as hidden argument to the function and
+no result is returned. A hidden result variable is used when the
+result variable is an array or of type @code{CHARACTER}.
+
+Arguments are passed according to the platform ABI. In particular,
+complex arguments might not be compatible to a struct with two real
+components for the real and imaginary part. The argument passing
+matches the one of C99's @code{_Complex}. Functions with scalar
+complex result variables return their value and do not use a
+by-reference argument. Note that with the @option{-ff2c} option,
+the argument passing is modified and no longer completely matches
+the platform ABI. Some other Fortran compilers use @code{f2c}
+semantic by default; this might cause problems with
+interoperablility.
+
+GNU Fortran passes most arguments by reference, i.e. by passing a
+pointer to the data. Note that the compiler might use a temporary
+variable into which the actual argument has been copied, if required
+semantically (copy-in/copy-out).
+
+For arguments with @code{ALLOCATABLE} and @code{POINTER}
+attribute (including procedure pointers), a pointer to the pointer
+is passed such that the pointer address can be modified in the
+procedure.
+
+For dummy arguments with the @code{VALUE} attribute: Scalar arguments
+of the type @code{INTEGER}, @code{LOGICAL}, @code{REAL} and
+@code{COMPLEX} are passed by value according to the platform ABI.
+(As vendor extension and not recommended, using @code{%VAL()} in the
+call to a procedure has the same effect.) For @code{TYPE(C_PTR)} and
+procedure pointers, the pointer itself is passed such that it can be
+modified without affecting the caller.
+@c FIXME: Document how VALUE is handled for CHARACTER, TYPE,
+@c CLASS and arrays, i.e. whether the copy-in is done in the caller
+@c or in the callee.
+
+For Boolean (@code{LOGICAL}) arguments, please note that GCC expects
+only the integer value 0 and 1. If a GNU Fortran @code{LOGICAL}
+variable contains another integer value, the result is undefined.
+As some other Fortran compilers use @math{-1} for @code{.TRUE.},
+extra care has to be taken -- such as passing the value as
+@code{INTEGER}. (The same value restriction also applies to other
+front ends of GCC, e.g. to GCC's C99 compiler for @code{_Bool}
+or GCC's Ada compiler for @code{Boolean}.)
+
+For arguments of @code{CHARACTER} type, the character length is passed
+as a hidden argument at the end of the argument list. For
+deferred-length strings, the value is passed by reference, otherwise
+by value. The character length has the C type @code{size_t} (or
+@code{INTEGER(kind=C_SIZE_T)} in Fortran). Note that this is
+different to older versions of the GNU Fortran compiler, where the
+type of the hidden character length argument was a C @code{int}. In
+order to retain compatibility with older versions, one can e.g. for
+the following Fortran procedure
+
+@smallexample
+subroutine fstrlen (s, a)
+ character(len=*) :: s
+ integer :: a
+ print*, len(s)
+end subroutine fstrlen
+@end smallexample
+
+define the corresponding C prototype as follows:
+
+@smallexample
+#if __GNUC__ > 7
+typedef size_t fortran_charlen_t;
+#else
+typedef int fortran_charlen_t;
+#endif
+
+void fstrlen_ (char*, int*, fortran_charlen_t);
+@end smallexample
+
+In order to avoid such compiler-specific details, for new code it is
+instead recommended to use the ISO_C_BINDING feature.
+
+Note with C binding, @code{CHARACTER(len=1)} result variables are
+returned according to the platform ABI and no hidden length argument
+is used for dummy arguments; with @code{VALUE}, those variables are
+passed by value.
+
+For @code{OPTIONAL} dummy arguments, an absent argument is denoted
+by a NULL pointer, except for scalar dummy arguments of type
+@code{INTEGER}, @code{LOGICAL}, @code{REAL} and @code{COMPLEX}
+which have the @code{VALUE} attribute. For those, a hidden Boolean
+argument (@code{logical(kind=C_bool),value}) is used to indicate
+whether the argument is present.
+
+Arguments which are assumed-shape, assumed-rank or deferred-rank
+arrays or, with @option{-fcoarray=lib}, allocatable scalar coarrays use
+an array descriptor. All other arrays pass the address of the
+first element of the array. With @option{-fcoarray=lib}, the token
+and the offset belonging to nonallocatable coarrays dummy arguments
+are passed as hidden argument along the character length hidden
+arguments. The token is an opaque pointer identifying the coarray
+and the offset is a passed-by-value integer of kind @code{C_PTRDIFF_T},
+denoting the byte offset between the base address of the coarray and
+the passed scalar or first element of the passed array.
+
+The arguments are passed in the following order
+@itemize @bullet
+@item Result variable, when the function result is passed by reference
+@item Character length of the function result, if it is a of type
+@code{CHARACTER} and no C binding is used
+@item The arguments in the order in which they appear in the Fortran
+declaration
+@item The the present status for optional arguments with value attribute,
+which are internally passed by value
+@item The character length and/or coarray token and offset for the first
+argument which is a @code{CHARACTER} or a nonallocatable coarray dummy
+argument, followed by the hidden arguments of the next dummy argument
+of such a type
+@end itemize
+
+
+@c ---------------------------------------------------------------------
+@c Coarray Programming
+@c ---------------------------------------------------------------------
+
+@node Coarray Programming
+@chapter Coarray Programming
+@cindex Coarrays
+
+@menu
+* Type and enum ABI Documentation::
+* Function ABI Documentation::
+@end menu
+
+
+@node Type and enum ABI Documentation
+@section Type and enum ABI Documentation
+
+@menu
+* caf_token_t::
+* caf_register_t::
+* caf_deregister_t::
+* caf_reference_t::
+* caf_team_t::
+@end menu
+
+@node caf_token_t
+@subsection @code{caf_token_t}
+
+Typedef of type @code{void *} on the compiler side. Can be any data
+type on the library side.
+
+@node caf_register_t
+@subsection @code{caf_register_t}
+
+Indicates which kind of coarray variable should be registered.
+
+@verbatim
+typedef enum caf_register_t {
+ CAF_REGTYPE_COARRAY_STATIC,
+ CAF_REGTYPE_COARRAY_ALLOC,
+ CAF_REGTYPE_LOCK_STATIC,
+ CAF_REGTYPE_LOCK_ALLOC,
+ CAF_REGTYPE_CRITICAL,
+ CAF_REGTYPE_EVENT_STATIC,
+ CAF_REGTYPE_EVENT_ALLOC,
+ CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY,
+ CAF_REGTYPE_COARRAY_ALLOC_ALLOCATE_ONLY
+}
+caf_register_t;
+@end verbatim
+
+The values @code{CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY} and
+@code{CAF_REGTYPE_COARRAY_ALLOC_ALLOCATE_ONLY} are for allocatable components
+in derived type coarrays only. The first one sets up the token without
+allocating memory for allocatable component. The latter one only allocates the
+memory for an allocatable component in a derived type coarray. The token
+needs to be setup previously by the REGISTER_ONLY. This allows to have
+allocatable components un-allocated on some images. The status whether an
+allocatable component is allocated on a remote image can be queried by
+@code{_caf_is_present} which used internally by the @code{ALLOCATED}
+intrinsic.
+
+@node caf_deregister_t
+@subsection @code{caf_deregister_t}
+
+@verbatim
+typedef enum caf_deregister_t {
+ CAF_DEREGTYPE_COARRAY_DEREGISTER,
+ CAF_DEREGTYPE_COARRAY_DEALLOCATE_ONLY
+}
+caf_deregister_t;
+@end verbatim
+
+Allows to specifiy the type of deregistration of a coarray object. The
+@code{CAF_DEREGTYPE_COARRAY_DEALLOCATE_ONLY} flag is only allowed for
+allocatable components in derived type coarrays.
+
+@node caf_reference_t
+@subsection @code{caf_reference_t}
+
+The structure used for implementing arbitrary reference chains.
+A @code{CAF_REFERENCE_T} allows to specify a component reference or any kind
+of array reference of any rank supported by gfortran. For array references all
+kinds as known by the compiler/Fortran standard are supported indicated by
+a @code{MODE}.
+
+@verbatim
+typedef enum caf_ref_type_t {
+ /* Reference a component of a derived type, either regular one or an
+ allocatable or pointer type. For regular ones idx in caf_reference_t is
+ set to -1. */
+ CAF_REF_COMPONENT,
+ /* Reference an allocatable array. */
+ CAF_REF_ARRAY,
+ /* Reference a non-allocatable/non-pointer array. I.e., the coarray object
+ has no array descriptor associated and the addressing is done
+ completely using the ref. */
+ CAF_REF_STATIC_ARRAY
+} caf_ref_type_t;
+@end verbatim
+
+@verbatim
+typedef enum caf_array_ref_t {
+ /* No array ref. This terminates the array ref. */
+ CAF_ARR_REF_NONE = 0,
+ /* Reference array elements given by a vector. Only for this mode
+ caf_reference_t.u.a.dim[i].v is valid. */
+ CAF_ARR_REF_VECTOR,
+ /* A full array ref (:). */
+ CAF_ARR_REF_FULL,
+ /* Reference a range on elements given by start, end and stride. */
+ CAF_ARR_REF_RANGE,
+ /* Only a single item is referenced given in the start member. */
+ CAF_ARR_REF_SINGLE,
+ /* An array ref of the kind (i:), where i is an arbitrary valid index in the
+ array. The index i is given in the start member. */
+ CAF_ARR_REF_OPEN_END,
+ /* An array ref of the kind (:i), where the lower bound of the array ref
+ is given by the remote side. The index i is given in the end member. */
+ CAF_ARR_REF_OPEN_START
+} caf_array_ref_t;
+@end verbatim
+
+@verbatim
+/* References to remote components of a derived type. */
+typedef struct caf_reference_t {
+ /* A pointer to the next ref or NULL. */
+ struct caf_reference_t *next;
+ /* The type of the reference. */
+ /* caf_ref_type_t, replaced by int to allow specification in fortran FE. */
+ int type;
+ /* The size of an item referenced in bytes. I.e. in an array ref this is
+ the factor to advance the array pointer with to get to the next item.
+ For component refs this gives just the size of the element referenced. */
+ size_t item_size;
+ union {
+ struct {
+ /* The offset (in bytes) of the component in the derived type.
+ Unused for allocatable or pointer components. */
+ ptrdiff_t offset;
+ /* The offset (in bytes) to the caf_token associated with this
+ component. NULL, when not allocatable/pointer ref. */
+ ptrdiff_t caf_token_offset;
+ } c;
+ struct {
+ /* The mode of the array ref. See CAF_ARR_REF_*. */
+ /* caf_array_ref_t, replaced by unsigend char to allow specification in
+ fortran FE. */
+ unsigned char mode[GFC_MAX_DIMENSIONS];
+ /* The type of a static array. Unset for array's with descriptors. */
+ int static_array_type;
+ /* Subscript refs (s) or vector refs (v). */
+ union {
+ struct {
+ /* The start and end boundary of the ref and the stride. */
+ index_type start, end, stride;
+ } s;
+ struct {
+ /* nvec entries of kind giving the elements to reference. */
+ void *vector;
+ /* The number of entries in vector. */
+ size_t nvec;
+ /* The integer kind used for the elements in vector. */
+ int kind;
+ } v;
+ } dim[GFC_MAX_DIMENSIONS];
+ } a;
+ } u;
+} caf_reference_t;
+@end verbatim
+
+The references make up a single linked list of reference operations. The
+@code{NEXT} member links to the next reference or NULL to indicate the end of
+the chain. Component and array refs can be arbitrarily mixed as long as they
+comply to the Fortran standard.
+
+@emph{NOTES}
+The member @code{STATIC_ARRAY_TYPE} is used only when the @code{TYPE} is
+@code{CAF_REF_STATIC_ARRAY}. The member gives the type of the data referenced.
+Because no array descriptor is available for a descriptor-less array and
+type conversion still needs to take place the type is transported here.
+
+At the moment @code{CAF_ARR_REF_VECTOR} is not implemented in the front end for
+descriptor-less arrays. The library caf_single has untested support for it.
+
+@node caf_team_t
+@subsection @code{caf_team_t}
+
+Opaque pointer to represent a team-handle. This type is a stand-in for the
+future implementation of teams. It is about to change without further notice.
+
+@node Function ABI Documentation
+@section Function ABI Documentation
+
+@menu
+* _gfortran_caf_init:: Initialiation function
+* _gfortran_caf_finish:: Finalization function
+* _gfortran_caf_this_image:: Querying the image number
+* _gfortran_caf_num_images:: Querying the maximal number of images
+* _gfortran_caf_image_status :: Query the status of an image
+* _gfortran_caf_failed_images :: Get an array of the indexes of the failed images
+* _gfortran_caf_stopped_images :: Get an array of the indexes of the stopped images
+* _gfortran_caf_register:: Registering coarrays
+* _gfortran_caf_deregister:: Deregistering coarrays
+* _gfortran_caf_is_present:: Query whether an allocatable or pointer component in a derived type coarray is allocated
+* _gfortran_caf_send:: Sending data from a local image to a remote image
+* _gfortran_caf_get:: Getting data from a remote image
+* _gfortran_caf_sendget:: Sending data between remote images
+* _gfortran_caf_send_by_ref:: Sending data from a local image to a remote image using enhanced references
+* _gfortran_caf_get_by_ref:: Getting data from a remote image using enhanced references
+* _gfortran_caf_sendget_by_ref:: Sending data between remote images using enhanced references
+* _gfortran_caf_lock:: Locking a lock variable
+* _gfortran_caf_unlock:: Unlocking a lock variable
+* _gfortran_caf_event_post:: Post an event
+* _gfortran_caf_event_wait:: Wait that an event occurred
+* _gfortran_caf_event_query:: Query event count
+* _gfortran_caf_sync_all:: All-image barrier
+* _gfortran_caf_sync_images:: Barrier for selected images
+* _gfortran_caf_sync_memory:: Wait for completion of segment-memory operations
+* _gfortran_caf_error_stop:: Error termination with exit code
+* _gfortran_caf_error_stop_str:: Error termination with string
+* _gfortran_caf_fail_image :: Mark the image failed and end its execution
+* _gfortran_caf_atomic_define:: Atomic variable assignment
+* _gfortran_caf_atomic_ref:: Atomic variable reference
+* _gfortran_caf_atomic_cas:: Atomic compare and swap
+* _gfortran_caf_atomic_op:: Atomic operation
+* _gfortran_caf_co_broadcast:: Sending data to all images
+* _gfortran_caf_co_max:: Collective maximum reduction
+* _gfortran_caf_co_min:: Collective minimum reduction
+* _gfortran_caf_co_sum:: Collective summing reduction
+* _gfortran_caf_co_reduce:: Generic collective reduction
+@end menu
+
+
+@node _gfortran_caf_init
+@subsection @code{_gfortran_caf_init} --- Initialiation function
+@cindex Coarray, _gfortran_caf_init
+
+@table @asis
+@item @emph{Description}:
+This function is called at startup of the program before the Fortran main
+program, if the latter has been compiled with @option{-fcoarray=lib}.
+It takes as arguments the command-line arguments of the program. It is
+permitted to pass two @code{NULL} pointers as argument; if non-@code{NULL},
+the library is permitted to modify the arguments.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_init (int *argc, char ***argv)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{argc} @tab intent(inout) An integer pointer with the number of
+arguments passed to the program or @code{NULL}.
+@item @var{argv} @tab intent(inout) A pointer to an array of strings with the
+command-line arguments or @code{NULL}.
+@end multitable
+
+@item @emph{NOTES}
+The function is modelled after the initialization function of the Message
+Passing Interface (MPI) specification. Due to the way coarray registration
+works, it might not be the first call to the library. If the main program is
+not written in Fortran and only a library uses coarrays, it can happen that
+this function is never called. Therefore, it is recommended that the library
+does not rely on the passed arguments and whether the call has been done.
+@end table
+
+
+@node _gfortran_caf_finish
+@subsection @code{_gfortran_caf_finish} --- Finalization function
+@cindex Coarray, _gfortran_caf_finish
+
+@table @asis
+@item @emph{Description}:
+This function is called at the end of the Fortran main program, if it has
+been compiled with the @option{-fcoarray=lib} option.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_finish (void)}
+
+@item @emph{NOTES}
+For non-Fortran programs, it is recommended to call the function at the end
+of the main program. To ensure that the shutdown is also performed for
+programs where this function is not explicitly invoked, for instance
+non-Fortran programs or calls to the system's exit() function, the library
+can use a destructor function. Note that programs can also be terminated
+using the STOP and ERROR STOP statements; those use different library calls.
+@end table
+
+
+@node _gfortran_caf_this_image
+@subsection @code{_gfortran_caf_this_image} --- Querying the image number
+@cindex Coarray, _gfortran_caf_this_image
+
+@table @asis
+@item @emph{Description}:
+This function returns the current image number, which is a positive number.
+
+@item @emph{Syntax}:
+@code{int _gfortran_caf_this_image (int distance)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{distance} @tab As specified for the @code{this_image} intrinsic
+in TS18508. Shall be a non-negative number.
+@end multitable
+
+@item @emph{NOTES}
+If the Fortran intrinsic @code{this_image} is invoked without an argument, which
+is the only permitted form in Fortran 2008, GCC passes @code{0} as
+first argument.
+@end table
+
+
+@node _gfortran_caf_num_images
+@subsection @code{_gfortran_caf_num_images} --- Querying the maximal number of images
+@cindex Coarray, _gfortran_caf_num_images
+
+@table @asis
+@item @emph{Description}:
+This function returns the number of images in the current team, if
+@var{distance} is 0 or the number of images in the parent team at the specified
+distance. If failed is -1, the function returns the number of all images at
+the specified distance; if it is 0, the function returns the number of
+nonfailed images, and if it is 1, it returns the number of failed images.
+
+@item @emph{Syntax}:
+@code{int _gfortran_caf_num_images(int distance, int failed)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{distance} @tab the distance from this image to the ancestor.
+Shall be positive.
+@item @var{failed} @tab shall be -1, 0, or 1
+@end multitable
+
+@item @emph{NOTES}
+This function follows TS18508. If the num_image intrinsic has no arguments,
+then the compiler passes @code{distance=0} and @code{failed=-1} to the function.
+@end table
+
+
+@node _gfortran_caf_image_status
+@subsection @code{_gfortran_caf_image_status} --- Query the status of an image
+@cindex Coarray, _gfortran_caf_image_status
+
+@table @asis
+@item @emph{Description}:
+Get the status of the image given by the id @var{image} of the team given by
+@var{team}. Valid results are zero, for image is ok, @code{STAT_STOPPED_IMAGE}
+from the ISO_FORTRAN_ENV module to indicate that the image has been stopped and
+@code{STAT_FAILED_IMAGE} also from ISO_FORTRAN_ENV to indicate that the image
+has executed a @code{FAIL IMAGE} statement.
+
+@item @emph{Syntax}:
+@code{int _gfortran_caf_image_status (int image, caf_team_t * team)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{image} @tab the positive scalar id of the image in the current TEAM.
+@item @var{team} @tab optional; team on the which the inquiry is to be
+performed.
+@end multitable
+
+@item @emph{NOTES}
+This function follows TS18508. Because team-functionality is not yet
+implemented a null-pointer is passed for the @var{team} argument at the moment.
+@end table
+
+
+@node _gfortran_caf_failed_images
+@subsection @code{_gfortran_caf_failed_images} --- Get an array of the indexes of the failed images
+@cindex Coarray, _gfortran_caf_failed_images
+
+@table @asis
+@item @emph{Description}:
+Get an array of image indexes in the current @var{team} that have failed. The
+array is sorted ascendingly. When @var{team} is not provided the current team
+is to be used. When @var{kind} is provided then the resulting array is of that
+integer kind else it is of default integer kind. The returns an unallocated
+size zero array when no images have failed.
+
+@item @emph{Syntax}:
+@code{int _gfortran_caf_failed_images (caf_team_t * team, int * kind)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{team} @tab optional; team on the which the inquiry is to be
+performed.
+@item @var{image} @tab optional; the kind of the resulting integer array.
+@end multitable
+
+@item @emph{NOTES}
+This function follows TS18508. Because team-functionality is not yet
+implemented a null-pointer is passed for the @var{team} argument at the moment.
+@end table
+
+
+@node _gfortran_caf_stopped_images
+@subsection @code{_gfortran_caf_stopped_images} --- Get an array of the indexes of the stopped images
+@cindex Coarray, _gfortran_caf_stopped_images
+
+@table @asis
+@item @emph{Description}:
+Get an array of image indexes in the current @var{team} that have stopped. The
+array is sorted ascendingly. When @var{team} is not provided the current team
+is to be used. When @var{kind} is provided then the resulting array is of that
+integer kind else it is of default integer kind. The returns an unallocated
+size zero array when no images have failed.
+
+@item @emph{Syntax}:
+@code{int _gfortran_caf_stopped_images (caf_team_t * team, int * kind)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{team} @tab optional; team on the which the inquiry is to be
+performed.
+@item @var{image} @tab optional; the kind of the resulting integer array.
+@end multitable
+
+@item @emph{NOTES}
+This function follows TS18508. Because team-functionality is not yet
+implemented a null-pointer is passed for the @var{team} argument at the moment.
+@end table
+
+
+@node _gfortran_caf_register
+@subsection @code{_gfortran_caf_register} --- Registering coarrays
+@cindex Coarray, _gfortran_caf_register
+
+@table @asis
+@item @emph{Description}:
+Registers memory for a coarray and creates a token to identify the coarray. The
+routine is called for both coarrays with @code{SAVE} attribute and using an
+explicit @code{ALLOCATE} statement. If an error occurs and @var{STAT} is a
+@code{NULL} pointer, the function shall abort with printing an error message
+and starting the error termination. If no error occurs and @var{STAT} is
+present, it shall be set to zero. Otherwise, it shall be set to a positive
+value and, if not-@code{NULL}, @var{ERRMSG} shall be set to a string describing
+the failure. The routine shall register the memory provided in the
+@code{DATA}-component of the array descriptor @var{DESC}, when that component
+is non-@code{NULL}, else it shall allocate sufficient memory and provide a
+pointer to it in the @code{DATA}-component of @var{DESC}. The array descriptor
+has rank zero, when a scalar object is to be registered and the array
+descriptor may be invalid after the call to @code{_gfortran_caf_register}.
+When an array is to be allocated the descriptor persists.
+
+For @code{CAF_REGTYPE_COARRAY_STATIC} and @code{CAF_REGTYPE_COARRAY_ALLOC},
+the passed size is the byte size requested. For @code{CAF_REGTYPE_LOCK_STATIC},
+@code{CAF_REGTYPE_LOCK_ALLOC} and @code{CAF_REGTYPE_CRITICAL} it is the array
+size or one for a scalar.
+
+When @code{CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY} is used, then only a token
+for an allocatable or pointer component is created. The @code{SIZE} parameter
+is not used then. On the contrary when
+@code{CAF_REGTYPE_COARRAY_ALLOC_ALLOCATE_ONLY} is specified, then the
+@var{token} needs to be registered by a previous call with regtype
+@code{CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY} and either the memory specified
+in the @var{DESC}'s data-ptr is registered or allocate when the data-ptr is
+@code{NULL}.
+
+@item @emph{Syntax}:
+@code{void caf_register (size_t size, caf_register_t type, caf_token_t *token,
+gfc_descriptor_t *desc, int *stat, char *errmsg, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{size} @tab For normal coarrays, the byte size of the coarray to be
+allocated; for lock types and event types, the number of elements.
+@item @var{type} @tab one of the caf_register_t types.
+@item @var{token} @tab intent(out) An opaque pointer identifying the coarray.
+@item @var{desc} @tab intent(inout) The (pseudo) array descriptor.
+@item @var{stat} @tab intent(out) For allocatable coarrays, stores the STAT=;
+may be @code{NULL}
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be @code{NULL}
+@item @var{errmsg_len} @tab the buffer size of errmsg.
+@end multitable
+
+@item @emph{NOTES}
+Nonallocatable coarrays have to be registered prior use from remote images.
+In order to guarantee this, they have to be registered before the main
+program. This can be achieved by creating constructor functions. That is what
+GCC does such that also for nonallocatable coarrays the memory is allocated and
+no static memory is used. The token permits to identify the coarray; to the
+processor, the token is a nonaliasing pointer. The library can, for instance,
+store the base address of the coarray in the token, some handle or a more
+complicated struct. The library may also store the array descriptor
+@var{DESC} when its rank is non-zero.
+
+For lock types, the value shall only be used for checking the allocation
+status. Note that for critical blocks, the locking is only required on one
+image; in the locking statement, the processor shall always pass an
+image index of one for critical-block lock variables
+(@code{CAF_REGTYPE_CRITICAL}). For lock types and critical-block variables,
+the initial value shall be unlocked (or, respectively, not in critical
+section) such as the value false; for event types, the initial state should
+be no event, e.g. zero.
+@end table
+
+
+@node _gfortran_caf_deregister
+@subsection @code{_gfortran_caf_deregister} --- Deregistering coarrays
+@cindex Coarray, _gfortran_caf_deregister
+
+@table @asis
+@item @emph{Description}:
+Called to free or deregister the memory of a coarray; the processor calls this
+function for automatic and explicit deallocation. In case of an error, this
+function shall fail with an error message, unless the @var{STAT} variable is
+not null. The library is only expected to free memory it allocated itself
+during a call to @code{_gfortran_caf_register}.
+
+@item @emph{Syntax}:
+@code{void caf_deregister (caf_token_t *token, caf_deregister_t type,
+int *stat, char *errmsg, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab the token to free.
+@item @var{type} @tab the type of action to take for the coarray. A
+@code{CAF_DEREGTYPE_COARRAY_DEALLOCATE_ONLY} is allowed only for allocatable or
+pointer components of derived type coarrays. The action only deallocates the
+local memory without deleting the token.
+@item @var{stat} @tab intent(out) Stores the STAT=; may be NULL
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set
+to an error message; may be NULL
+@item @var{errmsg_len} @tab the buffer size of errmsg.
+@end multitable
+
+@item @emph{NOTES}
+For nonalloatable coarrays this function is never called. If a cleanup is
+required, it has to be handled via the finish, stop and error stop functions,
+and via destructors.
+@end table
+
+
+@node _gfortran_caf_is_present
+@subsection @code{_gfortran_caf_is_present} --- Query whether an allocatable or pointer component in a derived type coarray is allocated
+@cindex Coarray, _gfortran_caf_is_present
+
+@table @asis
+@item @emph{Description}:
+Used to query the coarray library whether an allocatable component in a derived
+type coarray is allocated on a remote image.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_is_present (caf_token_t token, int image_index,
+gfc_reference_t *ref)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab An opaque pointer identifying the coarray.
+@item @var{image_index} @tab The ID of the remote image; must be a positive
+number.
+@item @var{ref} @tab A chain of references to address the allocatable or
+pointer component in the derived type coarray. The object reference needs to be
+a scalar or a full array reference, respectively.
+@end multitable
+
+@end table
+
+@node _gfortran_caf_send
+@subsection @code{_gfortran_caf_send} --- Sending data from a local image to a remote image
+@cindex Coarray, _gfortran_caf_send
+
+@table @asis
+@item @emph{Description}:
+Called to send a scalar, an array section or a whole array from a local
+to a remote image identified by the image_index.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_send (caf_token_t token, size_t offset,
+int image_index, gfc_descriptor_t *dest, caf_vector_t *dst_vector,
+gfc_descriptor_t *src, int dst_kind, int src_kind, bool may_require_tmp,
+int *stat)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{offset} @tab intent(in) By which amount of bytes the actual data is
+shifted compared to the base address of the coarray.
+@item @var{image_index} @tab intent(in) The ID of the remote image; must be a
+positive number.
+@item @var{dest} @tab intent(in) Array descriptor for the remote image for the
+bounds and the size. The @code{base_addr} shall not be accessed.
+@item @var{dst_vector} @tab intent(in) If not NULL, it contains the vector
+subscript of the destination array; the values are relative to the dimension
+triplet of the dest argument.
+@item @var{src} @tab intent(in) Array descriptor of the local array to be
+transferred to the remote image
+@item @var{dst_kind} @tab intent(in) Kind of the destination argument
+@item @var{src_kind} @tab intent(in) Kind of the source argument
+@item @var{may_require_tmp} @tab intent(in) The variable is @code{false} when
+it is known at compile time that the @var{dest} and @var{src} either cannot
+overlap or overlap (fully or partially) such that walking @var{src} and
+@var{dest} in element wise element order (honoring the stride value) will not
+lead to wrong results. Otherwise, the value is @code{true}.
+@item @var{stat} @tab intent(out) when non-NULL give the result of the
+operation, i.e., zero on success and non-zero on error. When NULL and an error
+occurs, then an error message is printed and the program is terminated.
+@end multitable
+
+@item @emph{NOTES}
+It is permitted to have @var{image_index} equal the current image; the memory
+of the send-to and the send-from might (partially) overlap in that case. The
+implementation has to take care that it handles this case, e.g. using
+@code{memmove} which handles (partially) overlapping memory. If
+@var{may_require_tmp} is true, the library might additionally create a
+temporary variable, unless additional checks show that this is not required
+(e.g. because walking backward is possible or because both arrays are
+contiguous and @code{memmove} takes care of overlap issues).
+
+Note that the assignment of a scalar to an array is permitted. In addition,
+the library has to handle numeric-type conversion and for strings, padding
+and different character kinds.
+@end table
+
+
+@node _gfortran_caf_get
+@subsection @code{_gfortran_caf_get} --- Getting data from a remote image
+@cindex Coarray, _gfortran_caf_get
+
+@table @asis
+@item @emph{Description}:
+Called to get an array section or a whole array from a remote,
+image identified by the image_index.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_get (caf_token_t token, size_t offset,
+int image_index, gfc_descriptor_t *src, caf_vector_t *src_vector,
+gfc_descriptor_t *dest, int src_kind, int dst_kind, bool may_require_tmp,
+int *stat)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{offset} @tab intent(in) By which amount of bytes the actual data is
+shifted compared to the base address of the coarray.
+@item @var{image_index} @tab intent(in) The ID of the remote image; must be a
+positive number.
+@item @var{dest} @tab intent(out) Array descriptor of the local array to store
+the data retrieved from the remote image
+@item @var{src} @tab intent(in) Array descriptor for the remote image for the
+bounds and the size. The @code{base_addr} shall not be accessed.
+@item @var{src_vector} @tab intent(in) If not NULL, it contains the vector
+subscript of the source array; the values are relative to the dimension
+triplet of the @var{src} argument.
+@item @var{dst_kind} @tab intent(in) Kind of the destination argument
+@item @var{src_kind} @tab intent(in) Kind of the source argument
+@item @var{may_require_tmp} @tab intent(in) The variable is @code{false} when
+it is known at compile time that the @var{dest} and @var{src} either cannot
+overlap or overlap (fully or partially) such that walking @var{src} and
+@var{dest} in element wise element order (honoring the stride value) will not
+lead to wrong results. Otherwise, the value is @code{true}.
+@item @var{stat} @tab intent(out) When non-NULL give the result of the
+operation, i.e., zero on success and non-zero on error. When NULL and an error
+occurs, then an error message is printed and the program is terminated.
+@end multitable
+
+@item @emph{NOTES}
+It is permitted to have @var{image_index} equal the current image; the memory of
+the send-to and the send-from might (partially) overlap in that case. The
+implementation has to take care that it handles this case, e.g. using
+@code{memmove} which handles (partially) overlapping memory. If
+@var{may_require_tmp} is true, the library might additionally create a
+temporary variable, unless additional checks show that this is not required
+(e.g. because walking backward is possible or because both arrays are
+contiguous and @code{memmove} takes care of overlap issues).
+
+Note that the library has to handle numeric-type conversion and for strings,
+padding and different character kinds.
+@end table
+
+
+@node _gfortran_caf_sendget
+@subsection @code{_gfortran_caf_sendget} --- Sending data between remote images
+@cindex Coarray, _gfortran_caf_sendget
+
+@table @asis
+@item @emph{Description}:
+Called to send a scalar, an array section or a whole array from a remote image
+identified by the @var{src_image_index} to a remote image identified by the
+@var{dst_image_index}.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_sendget (caf_token_t dst_token, size_t dst_offset,
+int dst_image_index, gfc_descriptor_t *dest, caf_vector_t *dst_vector,
+caf_token_t src_token, size_t src_offset, int src_image_index,
+gfc_descriptor_t *src, caf_vector_t *src_vector, int dst_kind, int src_kind,
+bool may_require_tmp, int *stat)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{dst_token} @tab intent(in) An opaque pointer identifying the
+destination coarray.
+@item @var{dst_offset} @tab intent(in) By which amount of bytes the actual data
+is shifted compared to the base address of the destination coarray.
+@item @var{dst_image_index} @tab intent(in) The ID of the destination remote
+image; must be a positive number.
+@item @var{dest} @tab intent(in) Array descriptor for the destination
+remote image for the bounds and the size. The @code{base_addr} shall not be
+accessed.
+@item @var{dst_vector} @tab intent(int) If not NULL, it contains the vector
+subscript of the destination array; the values are relative to the dimension
+triplet of the @var{dest} argument.
+@item @var{src_token} @tab intent(in) An opaque pointer identifying the source
+coarray.
+@item @var{src_offset} @tab intent(in) By which amount of bytes the actual data
+is shifted compared to the base address of the source coarray.
+@item @var{src_image_index} @tab intent(in) The ID of the source remote image;
+must be a positive number.
+@item @var{src} @tab intent(in) Array descriptor of the local array to be
+transferred to the remote image.
+@item @var{src_vector} @tab intent(in) Array descriptor of the local array to
+be transferred to the remote image
+@item @var{dst_kind} @tab intent(in) Kind of the destination argument
+@item @var{src_kind} @tab intent(in) Kind of the source argument
+@item @var{may_require_tmp} @tab intent(in) The variable is @code{false} when
+it is known at compile time that the @var{dest} and @var{src} either cannot
+overlap or overlap (fully or partially) such that walking @var{src} and
+@var{dest} in element wise element order (honoring the stride value) will not
+lead to wrong results. Otherwise, the value is @code{true}.
+@item @var{stat} @tab intent(out) when non-NULL give the result of the
+operation, i.e., zero on success and non-zero on error. When NULL and an error
+occurs, then an error message is printed and the program is terminated.
+@end multitable
+
+@item @emph{NOTES}
+It is permitted to have the same image index for both @var{src_image_index} and
+@var{dst_image_index}; the memory of the send-to and the send-from might
+(partially) overlap in that case. The implementation has to take care that it
+handles this case, e.g. using @code{memmove} which handles (partially)
+overlapping memory. If @var{may_require_tmp} is true, the library
+might additionally create a temporary variable, unless additional checks show
+that this is not required (e.g. because walking backward is possible or because
+both arrays are contiguous and @code{memmove} takes care of overlap issues).
+
+Note that the assignment of a scalar to an array is permitted. In addition,
+the library has to handle numeric-type conversion and for strings, padding and
+different character kinds.
+@end table
+
+@node _gfortran_caf_send_by_ref
+@subsection @code{_gfortran_caf_send_by_ref} --- Sending data from a local image to a remote image with enhanced referencing options
+@cindex Coarray, _gfortran_caf_send_by_ref
+
+@table @asis
+@item @emph{Description}:
+Called to send a scalar, an array section or a whole array from a local to a
+remote image identified by the @var{image_index}.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_send_by_ref (caf_token_t token, int image_index,
+gfc_descriptor_t *src, caf_reference_t *refs, int dst_kind, int src_kind,
+bool may_require_tmp, bool dst_reallocatable, int *stat, int dst_type)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{image_index} @tab intent(in) The ID of the remote image; must be a
+positive number.
+@item @var{src} @tab intent(in) Array descriptor of the local array to be
+transferred to the remote image
+@item @var{refs} @tab intent(in) The references on the remote array to store
+the data given by src. Guaranteed to have at least one entry.
+@item @var{dst_kind} @tab intent(in) Kind of the destination argument
+@item @var{src_kind} @tab intent(in) Kind of the source argument
+@item @var{may_require_tmp} @tab intent(in) The variable is @code{false} when
+it is known at compile time that the @var{dest} and @var{src} either cannot
+overlap or overlap (fully or partially) such that walking @var{src} and
+@var{dest} in element wise element order (honoring the stride value) will not
+lead to wrong results. Otherwise, the value is @code{true}.
+@item @var{dst_reallocatable} @tab intent(in) Set when the destination is of
+allocatable or pointer type and the refs will allow reallocation, i.e., the ref
+is a full array or component ref.
+@item @var{stat} @tab intent(out) When non-@code{NULL} give the result of the
+operation, i.e., zero on success and non-zero on error. When @code{NULL} and
+an error occurs, then an error message is printed and the program is terminated.
+@item @var{dst_type} @tab intent(in) Give the type of the destination. When
+the destination is not an array, than the precise type, e.g. of a component in
+a derived type, is not known, but provided here.
+@end multitable
+
+@item @emph{NOTES}
+It is permitted to have @var{image_index} equal the current image; the memory of
+the send-to and the send-from might (partially) overlap in that case. The
+implementation has to take care that it handles this case, e.g. using
+@code{memmove} which handles (partially) overlapping memory. If
+@var{may_require_tmp} is true, the library might additionally create a
+temporary variable, unless additional checks show that this is not required
+(e.g. because walking backward is possible or because both arrays are
+contiguous and @code{memmove} takes care of overlap issues).
+
+Note that the assignment of a scalar to an array is permitted. In addition,
+the library has to handle numeric-type conversion and for strings, padding
+and different character kinds.
+
+Because of the more complicated references possible some operations may be
+unsupported by certain libraries. The library is expected to issue a precise
+error message why the operation is not permitted.
+@end table
+
+
+@node _gfortran_caf_get_by_ref
+@subsection @code{_gfortran_caf_get_by_ref} --- Getting data from a remote image using enhanced references
+@cindex Coarray, _gfortran_caf_get_by_ref
+
+@table @asis
+@item @emph{Description}:
+Called to get a scalar, an array section or a whole array from a remote image
+identified by the @var{image_index}.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_get_by_ref (caf_token_t token, int image_index,
+caf_reference_t *refs, gfc_descriptor_t *dst, int dst_kind, int src_kind,
+bool may_require_tmp, bool dst_reallocatable, int *stat, int src_type)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{image_index} @tab intent(in) The ID of the remote image; must be a
+positive number.
+@item @var{refs} @tab intent(in) The references to apply to the remote structure
+to get the data.
+@item @var{dst} @tab intent(in) Array descriptor of the local array to store
+the data transferred from the remote image. May be reallocated where needed
+and when @var{DST_REALLOCATABLE} allows it.
+@item @var{dst_kind} @tab intent(in) Kind of the destination argument
+@item @var{src_kind} @tab intent(in) Kind of the source argument
+@item @var{may_require_tmp} @tab intent(in) The variable is @code{false} when
+it is known at compile time that the @var{dest} and @var{src} either cannot
+overlap or overlap (fully or partially) such that walking @var{src} and
+@var{dest} in element wise element order (honoring the stride value) will not
+lead to wrong results. Otherwise, the value is @code{true}.
+@item @var{dst_reallocatable} @tab intent(in) Set when @var{DST} is of
+allocatable or pointer type and its refs allow reallocation, i.e., the full
+array or a component is referenced.
+@item @var{stat} @tab intent(out) When non-@code{NULL} give the result of the
+operation, i.e., zero on success and non-zero on error. When @code{NULL} and an
+error occurs, then an error message is printed and the program is terminated.
+@item @var{src_type} @tab intent(in) Give the type of the source. When the
+source is not an array, than the precise type, e.g. of a component in a
+derived type, is not known, but provided here.
+@end multitable
+
+@item @emph{NOTES}
+It is permitted to have @code{image_index} equal the current image; the memory
+of the send-to and the send-from might (partially) overlap in that case. The
+implementation has to take care that it handles this case, e.g. using
+@code{memmove} which handles (partially) overlapping memory. If
+@var{may_require_tmp} is true, the library might additionally create a
+temporary variable, unless additional checks show that this is not required
+(e.g. because walking backward is possible or because both arrays are
+contiguous and @code{memmove} takes care of overlap issues).
+
+Note that the library has to handle numeric-type conversion and for strings,
+padding and different character kinds.
+
+Because of the more complicated references possible some operations may be
+unsupported by certain libraries. The library is expected to issue a precise
+error message why the operation is not permitted.
+@end table
+
+
+@node _gfortran_caf_sendget_by_ref
+@subsection @code{_gfortran_caf_sendget_by_ref} --- Sending data between remote images using enhanced references on both sides
+@cindex Coarray, _gfortran_caf_sendget_by_ref
+
+@table @asis
+@item @emph{Description}:
+Called to send a scalar, an array section or a whole array from a remote image
+identified by the @var{src_image_index} to a remote image identified by the
+@var{dst_image_index}.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_sendget_by_ref (caf_token_t dst_token,
+int dst_image_index, caf_reference_t *dst_refs,
+caf_token_t src_token, int src_image_index, caf_reference_t *src_refs,
+int dst_kind, int src_kind, bool may_require_tmp, int *dst_stat,
+int *src_stat, int dst_type, int src_type)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{dst_token} @tab intent(in) An opaque pointer identifying the
+destination coarray.
+@item @var{dst_image_index} @tab intent(in) The ID of the destination remote
+image; must be a positive number.
+@item @var{dst_refs} @tab intent(in) The references on the remote array to store
+the data given by the source. Guaranteed to have at least one entry.
+@item @var{src_token} @tab intent(in) An opaque pointer identifying the source
+coarray.
+@item @var{src_image_index} @tab intent(in) The ID of the source remote image;
+must be a positive number.
+@item @var{src_refs} @tab intent(in) The references to apply to the remote
+structure to get the data.
+@item @var{dst_kind} @tab intent(in) Kind of the destination argument
+@item @var{src_kind} @tab intent(in) Kind of the source argument
+@item @var{may_require_tmp} @tab intent(in) The variable is @code{false} when
+it is known at compile time that the @var{dest} and @var{src} either cannot
+overlap or overlap (fully or partially) such that walking @var{src} and
+@var{dest} in element wise element order (honoring the stride value) will not
+lead to wrong results. Otherwise, the value is @code{true}.
+@item @var{dst_stat} @tab intent(out) when non-@code{NULL} give the result of
+the send-operation, i.e., zero on success and non-zero on error. When
+@code{NULL} and an error occurs, then an error message is printed and the
+program is terminated.
+@item @var{src_stat} @tab intent(out) When non-@code{NULL} give the result of
+the get-operation, i.e., zero on success and non-zero on error. When
+@code{NULL} and an error occurs, then an error message is printed and the
+program is terminated.
+@item @var{dst_type} @tab intent(in) Give the type of the destination. When
+the destination is not an array, than the precise type, e.g. of a component in
+a derived type, is not known, but provided here.
+@item @var{src_type} @tab intent(in) Give the type of the source. When the
+source is not an array, than the precise type, e.g. of a component in a
+derived type, is not known, but provided here.
+@end multitable
+
+@item @emph{NOTES}
+It is permitted to have the same image index for both @var{src_image_index} and
+@var{dst_image_index}; the memory of the send-to and the send-from might
+(partially) overlap in that case. The implementation has to take care that it
+handles this case, e.g. using @code{memmove} which handles (partially)
+overlapping memory. If @var{may_require_tmp} is true, the library
+might additionally create a temporary variable, unless additional checks show
+that this is not required (e.g. because walking backward is possible or because
+both arrays are contiguous and @code{memmove} takes care of overlap issues).
+
+Note that the assignment of a scalar to an array is permitted. In addition,
+the library has to handle numeric-type conversion and for strings, padding and
+different character kinds.
+
+Because of the more complicated references possible some operations may be
+unsupported by certain libraries. The library is expected to issue a precise
+error message why the operation is not permitted.
+@end table
+
+
+@node _gfortran_caf_lock
+@subsection @code{_gfortran_caf_lock} --- Locking a lock variable
+@cindex Coarray, _gfortran_caf_lock
+
+@table @asis
+@item @emph{Description}:
+Acquire a lock on the given image on a scalar locking variable or for the
+given array element for an array-valued variable. If the @var{acquired_lock}
+is @code{NULL}, the function returns after having obtained the lock. If it is
+non-@code{NULL}, then @var{acquired_lock} is assigned the value true (one) when
+the lock could be obtained and false (zero) otherwise. Locking a lock variable
+which has already been locked by the same image is an error.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_lock (caf_token_t token, size_t index, int image_index,
+int *acquired_lock, int *stat, char *errmsg, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{index} @tab intent(in) Array index; first array index is 0. For
+scalars, it is always 0.
+@item @var{image_index} @tab intent(in) The ID of the remote image; must be a
+positive number.
+@item @var{acquired_lock} @tab intent(out) If not NULL, it returns whether lock
+could be obtained.
+@item @var{stat} @tab intent(out) Stores the STAT=; may be NULL.
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be NULL.
+@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg
+@end multitable
+
+@item @emph{NOTES}
+This function is also called for critical blocks; for those, the array index
+is always zero and the image index is one. Libraries are permitted to use other
+images for critical-block locking variables.
+@end table
+
+@node _gfortran_caf_unlock
+@subsection @code{_gfortran_caf_lock} --- Unlocking a lock variable
+@cindex Coarray, _gfortran_caf_unlock
+
+@table @asis
+@item @emph{Description}:
+Release a lock on the given image on a scalar locking variable or for the
+given array element for an array-valued variable. Unlocking a lock variable
+which is unlocked or has been locked by a different image is an error.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_unlock (caf_token_t token, size_t index, int image_index,
+int *stat, char *errmsg, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{index} @tab intent(in) Array index; first array index is 0. For
+scalars, it is always 0.
+@item @var{image_index} @tab intent(in) The ID of the remote image; must be a
+positive number.
+@item @var{stat} @tab intent(out) For allocatable coarrays, stores the STAT=;
+may be NULL.
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be NULL.
+@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg
+@end multitable
+
+@item @emph{NOTES}
+This function is also called for critical block; for those, the array index
+is always zero and the image index is one. Libraries are permitted to use other
+images for critical-block locking variables.
+@end table
+
+@node _gfortran_caf_event_post
+@subsection @code{_gfortran_caf_event_post} --- Post an event
+@cindex Coarray, _gfortran_caf_event_post
+
+@table @asis
+@item @emph{Description}:
+Increment the event count of the specified event variable.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_event_post (caf_token_t token, size_t index,
+int image_index, int *stat, char *errmsg, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{index} @tab intent(in) Array index; first array index is 0. For
+scalars, it is always 0.
+@item @var{image_index} @tab intent(in) The ID of the remote image; must be a
+positive number; zero indicates the current image, when accessed noncoindexed.
+@item @var{stat} @tab intent(out) Stores the STAT=; may be NULL.
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be NULL.
+@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg
+@end multitable
+
+@item @emph{NOTES}
+This acts like an atomic add of one to the remote image's event variable.
+The statement is an image-control statement but does not imply sync memory.
+Still, all preceeding push communications of this image to the specified
+remote image have to be completed before @code{event_wait} on the remote
+image returns.
+@end table
+
+
+
+@node _gfortran_caf_event_wait
+@subsection @code{_gfortran_caf_event_wait} --- Wait that an event occurred
+@cindex Coarray, _gfortran_caf_event_wait
+
+@table @asis
+@item @emph{Description}:
+Wait until the event count has reached at least the specified
+@var{until_count}; if so, atomically decrement the event variable by this
+amount and return.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_event_wait (caf_token_t token, size_t index,
+int until_count, int *stat, char *errmsg, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{index} @tab intent(in) Array index; first array index is 0. For
+scalars, it is always 0.
+@item @var{until_count} @tab intent(in) The number of events which have to be
+available before the function returns.
+@item @var{stat} @tab intent(out) Stores the STAT=; may be NULL.
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be NULL.
+@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg
+@end multitable
+
+@item @emph{NOTES}
+This function only operates on a local coarray. It acts like a loop checking
+atomically the value of the event variable, breaking if the value is greater
+or equal the requested number of counts. Before the function returns, the
+event variable has to be decremented by the requested @var{until_count} value.
+A possible implementation would be a busy loop for a certain number of spins
+(possibly depending on the number of threads relative to the number of available
+cores) followed by another waiting strategy such as a sleeping wait (possibly
+with an increasing number of sleep time) or, if possible, a futex wait.
+
+The statement is an image-control statement but does not imply sync memory.
+Still, all preceeding push communications of this image to the specified
+remote image have to be completed before @code{event_wait} on the remote
+image returns.
+@end table
+
+
+
+@node _gfortran_caf_event_query
+@subsection @code{_gfortran_caf_event_query} --- Query event count
+@cindex Coarray, _gfortran_caf_event_query
+
+@table @asis
+@item @emph{Description}:
+Return the event count of the specified event variable.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_event_query (caf_token_t token, size_t index,
+int image_index, int *count, int *stat)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{index} @tab intent(in) Array index; first array index is 0. For
+scalars, it is always 0.
+@item @var{image_index} @tab intent(in) The ID of the remote image; must be a
+positive number; zero indicates the current image when accessed noncoindexed.
+@item @var{count} @tab intent(out) The number of events currently posted to
+the event variable.
+@item @var{stat} @tab intent(out) Stores the STAT=; may be NULL.
+@end multitable
+
+@item @emph{NOTES}
+The typical use is to check the local event variable to only call
+@code{event_wait} when the data is available. However, a coindexed variable
+is permitted; there is no ordering or synchronization implied. It acts like
+an atomic fetch of the value of the event variable.
+@end table
+
+
+
+@node _gfortran_caf_sync_all
+@subsection @code{_gfortran_caf_sync_all} --- All-image barrier
+@cindex Coarray, _gfortran_caf_sync_all
+
+@table @asis
+@item @emph{Description}:
+Synchronization of all images in the current team; the program only continues
+on a given image after this function has been called on all images of the
+current team. Additionally, it ensures that all pending data transfers of
+previous segment have completed.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_sync_all (int *stat, char *errmsg, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL.
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be NULL.
+@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg
+@end multitable
+@end table
+
+
+
+@node _gfortran_caf_sync_images
+@subsection @code{_gfortran_caf_sync_images} --- Barrier for selected images
+@cindex Coarray, _gfortran_caf_sync_images
+
+@table @asis
+@item @emph{Description}:
+Synchronization between the specified images; the program only continues on a
+given image after this function has been called on all images specified for
+that image. Note that one image can wait for all other images in the current
+team (e.g. via @code{sync images(*)}) while those only wait for that specific
+image. Additionally, @code{sync images} ensures that all pending data
+transfers of previous segments have completed.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_sync_images (int count, int images[], int *stat,
+char *errmsg, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{count} @tab intent(in) The number of images which are provided in
+the next argument. For a zero-sized array, the value is zero. For
+@code{sync images (*)}, the value is @math{-1}.
+@item @var{images} @tab intent(in) An array with the images provided by the
+user. If @var{count} is zero, a NULL pointer is passed.
+@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL.
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be NULL.
+@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg
+@end multitable
+@end table
+
+
+
+@node _gfortran_caf_sync_memory
+@subsection @code{_gfortran_caf_sync_memory} --- Wait for completion of segment-memory operations
+@cindex Coarray, _gfortran_caf_sync_memory
+
+@table @asis
+@item @emph{Description}:
+Acts as optimization barrier between different segments. It also ensures that
+all pending memory operations of this image have been completed.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_sync_memory (int *stat, char *errmsg, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL.
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be NULL.
+@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg
+@end multitable
+
+@item @emph{NOTE} A simple implementation could be
+@code{__asm__ __volatile__ ("":::"memory")} to prevent code movements.
+@end table
+
+
+
+@node _gfortran_caf_error_stop
+@subsection @code{_gfortran_caf_error_stop} --- Error termination with exit code
+@cindex Coarray, _gfortran_caf_error_stop
+
+@table @asis
+@item @emph{Description}:
+Invoked for an @code{ERROR STOP} statement which has an integer argument. The
+function should terminate the program with the specified exit code.
+
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_error_stop (int error)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{error} @tab intent(in) The exit status to be used.
+@end multitable
+@end table
+
+
+
+@node _gfortran_caf_error_stop_str
+@subsection @code{_gfortran_caf_error_stop_str} --- Error termination with string
+@cindex Coarray, _gfortran_caf_error_stop_str
+
+@table @asis
+@item @emph{Description}:
+Invoked for an @code{ERROR STOP} statement which has a string as argument. The
+function should terminate the program with a nonzero-exit code.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_error_stop (const char *string, size_t len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{string} @tab intent(in) the error message (not zero terminated)
+@item @var{len} @tab intent(in) the length of the string
+@end multitable
+@end table
+
+
+
+@node _gfortran_caf_fail_image
+@subsection @code{_gfortran_caf_fail_image} --- Mark the image failed and end its execution
+@cindex Coarray, _gfortran_caf_fail_image
+
+@table @asis
+@item @emph{Description}:
+Invoked for an @code{FAIL IMAGE} statement. The function should terminate the
+current image.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_fail_image ()}
+
+@item @emph{NOTES}
+This function follows TS18508.
+@end table
+
+
+
+@node _gfortran_caf_atomic_define
+@subsection @code{_gfortran_caf_atomic_define} --- Atomic variable assignment
+@cindex Coarray, _gfortran_caf_atomic_define
+
+@table @asis
+@item @emph{Description}:
+Assign atomically a value to an integer or logical variable.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_atomic_define (caf_token_t token, size_t offset,
+int image_index, void *value, int *stat, int type, int kind)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{offset} @tab intent(in) By which amount of bytes the actual data is
+shifted compared to the base address of the coarray.
+@item @var{image_index} @tab intent(in) The ID of the remote image; must be a
+positive number; zero indicates the current image when used noncoindexed.
+@item @var{value} @tab intent(in) the value to be assigned, passed by reference
+@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL.
+@item @var{type} @tab intent(in) The data type, i.e. @code{BT_INTEGER} (1) or
+@code{BT_LOGICAL} (2).
+@item @var{kind} @tab intent(in) The kind value (only 4; always @code{int})
+@end multitable
+@end table
+
+
+
+@node _gfortran_caf_atomic_ref
+@subsection @code{_gfortran_caf_atomic_ref} --- Atomic variable reference
+@cindex Coarray, _gfortran_caf_atomic_ref
+
+@table @asis
+@item @emph{Description}:
+Reference atomically a value of a kind-4 integer or logical variable.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_atomic_ref (caf_token_t token, size_t offset,
+int image_index, void *value, int *stat, int type, int kind)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{offset} @tab intent(in) By which amount of bytes the actual data is
+shifted compared to the base address of the coarray.
+@item @var{image_index} @tab intent(in) The ID of the remote image; must be a
+positive number; zero indicates the current image when used noncoindexed.
+@item @var{value} @tab intent(out) The variable assigned the atomically
+referenced variable.
+@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL.
+@item @var{type} @tab the data type, i.e. @code{BT_INTEGER} (1) or
+@code{BT_LOGICAL} (2).
+@item @var{kind} @tab The kind value (only 4; always @code{int})
+@end multitable
+@end table
+
+
+
+@node _gfortran_caf_atomic_cas
+@subsection @code{_gfortran_caf_atomic_cas} --- Atomic compare and swap
+@cindex Coarray, _gfortran_caf_atomic_cas
+
+@table @asis
+@item @emph{Description}:
+Atomic compare and swap of a kind-4 integer or logical variable. Assigns
+atomically the specified value to the atomic variable, if the latter has
+the value specified by the passed condition value.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_atomic_cas (caf_token_t token, size_t offset,
+int image_index, void *old, void *compare, void *new_val, int *stat,
+int type, int kind)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{offset} @tab intent(in) By which amount of bytes the actual data is
+shifted compared to the base address of the coarray.
+@item @var{image_index} @tab intent(in) The ID of the remote image; must be a
+positive number; zero indicates the current image when used noncoindexed.
+@item @var{old} @tab intent(out) The value which the atomic variable had
+just before the cas operation.
+@item @var{compare} @tab intent(in) The value used for comparision.
+@item @var{new_val} @tab intent(in) The new value for the atomic variable,
+assigned to the atomic variable, if @code{compare} equals the value of the
+atomic variable.
+@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL.
+@item @var{type} @tab intent(in) the data type, i.e. @code{BT_INTEGER} (1) or
+@code{BT_LOGICAL} (2).
+@item @var{kind} @tab intent(in) The kind value (only 4; always @code{int})
+@end multitable
+@end table
+
+
+
+@node _gfortran_caf_atomic_op
+@subsection @code{_gfortran_caf_atomic_op} --- Atomic operation
+@cindex Coarray, _gfortran_caf_atomic_op
+
+@table @asis
+@item @emph{Description}:
+Apply an operation atomically to an atomic integer or logical variable.
+After the operation, @var{old} contains the value just before the operation,
+which, respectively, adds (GFC_CAF_ATOMIC_ADD) atomically the @code{value} to
+the atomic integer variable or does a bitwise AND, OR or exclusive OR
+between the atomic variable and @var{value}; the result is then stored in the
+atomic variable.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_atomic_op (int op, caf_token_t token, size_t offset,
+int image_index, void *value, void *old, int *stat, int type, int kind)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{op} @tab intent(in) the operation to be performed; possible values
+@code{GFC_CAF_ATOMIC_ADD} (1), @code{GFC_CAF_ATOMIC_AND} (2),
+@code{GFC_CAF_ATOMIC_OR} (3), @code{GFC_CAF_ATOMIC_XOR} (4).
+@item @var{token} @tab intent(in) An opaque pointer identifying the coarray.
+@item @var{offset} @tab intent(in) By which amount of bytes the actual data is
+shifted compared to the base address of the coarray.
+@item @var{image_index} @tab intent(in) The ID of the remote image; must be a
+positive number; zero indicates the current image when used noncoindexed.
+@item @var{old} @tab intent(out) The value which the atomic variable had
+just before the atomic operation.
+@item @var{val} @tab intent(in) The new value for the atomic variable,
+assigned to the atomic variable, if @code{compare} equals the value of the
+atomic variable.
+@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL.
+@item @var{type} @tab intent(in) the data type, i.e. @code{BT_INTEGER} (1) or
+@code{BT_LOGICAL} (2)
+@item @var{kind} @tab intent(in) the kind value (only 4; always @code{int})
+@end multitable
+@end table
+
+
+
+
+@node _gfortran_caf_co_broadcast
+@subsection @code{_gfortran_caf_co_broadcast} --- Sending data to all images
+@cindex Coarray, _gfortran_caf_co_broadcast
+
+@table @asis
+@item @emph{Description}:
+Distribute a value from a given image to all other images in the team. Has to
+be called collectively.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_co_broadcast (gfc_descriptor_t *a,
+int source_image, int *stat, char *errmsg, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{a} @tab intent(inout) An array descriptor with the data to be
+broadcasted (on @var{source_image}) or to be received (other images).
+@item @var{source_image} @tab intent(in) The ID of the image from which the
+data should be broadcasted.
+@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL.
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be NULL.
+@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg.
+@end multitable
+@end table
+
+
+
+@node _gfortran_caf_co_max
+@subsection @code{_gfortran_caf_co_max} --- Collective maximum reduction
+@cindex Coarray, _gfortran_caf_co_max
+
+@table @asis
+@item @emph{Description}:
+Calculates for each array element of the variable @var{a} the maximum
+value for that element in the current team; if @var{result_image} has the
+value 0, the result shall be stored on all images, otherwise, only on the
+specified image. This function operates on numeric values and character
+strings.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_co_max (gfc_descriptor_t *a, int result_image,
+int *stat, char *errmsg, int a_len, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{a} @tab intent(inout) An array descriptor for the data to be
+processed. On the destination image(s) the result overwrites the old content.
+@item @var{result_image} @tab intent(in) The ID of the image to which the
+reduced value should be copied to; if zero, it has to be copied to all images.
+@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL.
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be NULL.
+@item @var{a_len} @tab intent(in) the string length of argument @var{a}
+@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg
+@end multitable
+
+@item @emph{NOTES}
+If @var{result_image} is nonzero, the data in the array descriptor @var{a} on
+all images except of the specified one become undefined; hence, the library may
+make use of this.
+@end table
+
+
+
+@node _gfortran_caf_co_min
+@subsection @code{_gfortran_caf_co_min} --- Collective minimum reduction
+@cindex Coarray, _gfortran_caf_co_min
+
+@table @asis
+@item @emph{Description}:
+Calculates for each array element of the variable @var{a} the minimum
+value for that element in the current team; if @var{result_image} has the
+value 0, the result shall be stored on all images, otherwise, only on the
+specified image. This function operates on numeric values and character
+strings.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_co_min (gfc_descriptor_t *a, int result_image,
+int *stat, char *errmsg, int a_len, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{a} @tab intent(inout) An array descriptor for the data to be
+processed. On the destination image(s) the result overwrites the old content.
+@item @var{result_image} @tab intent(in) The ID of the image to which the
+reduced value should be copied to; if zero, it has to be copied to all images.
+@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL.
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be NULL.
+@item @var{a_len} @tab intent(in) the string length of argument @var{a}
+@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg
+@end multitable
+
+@item @emph{NOTES}
+If @var{result_image} is nonzero, the data in the array descriptor @var{a} on
+all images except of the specified one become undefined; hence, the library may
+make use of this.
+@end table
+
+
+
+@node _gfortran_caf_co_sum
+@subsection @code{_gfortran_caf_co_sum} --- Collective summing reduction
+@cindex Coarray, _gfortran_caf_co_sum
+
+@table @asis
+@item @emph{Description}:
+Calculates for each array element of the variable @var{a} the sum of all
+values for that element in the current team; if @var{result_image} has the
+value 0, the result shall be stored on all images, otherwise, only on the
+specified image. This function operates on numeric values only.
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_co_sum (gfc_descriptor_t *a, int result_image,
+int *stat, char *errmsg, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{a} @tab intent(inout) An array descriptor with the data to be
+processed. On the destination image(s) the result overwrites the old content.
+@item @var{result_image} @tab intent(in) The ID of the image to which the
+reduced value should be copied to; if zero, it has to be copied to all images.
+@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL.
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be NULL.
+@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg
+@end multitable
+
+@item @emph{NOTES}
+If @var{result_image} is nonzero, the data in the array descriptor @var{a} on
+all images except of the specified one become undefined; hence, the library may
+make use of this.
+@end table
+
+
+
+@node _gfortran_caf_co_reduce
+@subsection @code{_gfortran_caf_co_reduce} --- Generic collective reduction
+@cindex Coarray, _gfortran_caf_co_reduce
+
+@table @asis
+@item @emph{Description}:
+Calculates for each array element of the variable @var{a} the reduction
+value for that element in the current team; if @var{result_image} has the
+value 0, the result shall be stored on all images, otherwise, only on the
+specified image. The @var{opr} is a pure function doing a mathematically
+commutative and associative operation.
+
+The @var{opr_flags} denote the following; the values are bitwise ored.
+@code{GFC_CAF_BYREF} (1) if the result should be returned
+by reference; @code{GFC_CAF_HIDDENLEN} (2) whether the result and argument
+string lengths shall be specified as hidden arguments;
+@code{GFC_CAF_ARG_VALUE} (4) whether the arguments shall be passed by value,
+@code{GFC_CAF_ARG_DESC} (8) whether the arguments shall be passed by descriptor.
+
+
+@item @emph{Syntax}:
+@code{void _gfortran_caf_co_reduce (gfc_descriptor_t *a,
+void * (*opr) (void *, void *), int opr_flags, int result_image,
+int *stat, char *errmsg, int a_len, size_t errmsg_len)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{a} @tab intent(inout) An array descriptor with the data to be
+processed. On the destination image(s) the result overwrites the old content.
+@item @var{opr} @tab intent(in) Function pointer to the reduction function
+@item @var{opr_flags} @tab intent(in) Flags regarding the reduction function
+@item @var{result_image} @tab intent(in) The ID of the image to which the
+reduced value should be copied to; if zero, it has to be copied to all images.
+@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL.
+@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to
+an error message; may be NULL.
+@item @var{a_len} @tab intent(in) the string length of argument @var{a}
+@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg
+@end multitable
+
+@item @emph{NOTES}
+If @var{result_image} is nonzero, the data in the array descriptor @var{a} on
+all images except of the specified one become undefined; hence, the library may
+make use of this.
+
+For character arguments, the result is passed as first argument, followed
+by the result string length, next come the two string arguments, followed
+by the two hidden string length arguments. With C binding, there are no hidden
+arguments and by-reference passing and either only a single character is passed
+or an array descriptor.
+@end table
+
+
+@c Intrinsic Procedures
+@c ---------------------------------------------------------------------
+
+@include intrinsic.texi
+
+
+@tex
+\blankpart
+@end tex
+
+@c ---------------------------------------------------------------------
@c Contributing
@c ---------------------------------------------------------------------
happening on GNU Fortran,
but others are ``mainstream'' projects in need of enthusiastic hackers.
All of these projects are important!
-We'll eventually get around to the things here,
+We will eventually get around to the things here,
but they are also things doable by someone who is willing and able.
@menu
@item Andy Vaught
@item Feng Wang
@item Janus Weil
+@item Daniel Kraft
@end itemize
The following people have contributed bug reports,
smaller or larger patches,
and much needed feedback and encouragement for the
-GNU Fortran project:
+GNU Fortran project:
@itemize @minus
@item Bill Clodius
@item Dominique d'Humi@`eres
@item Kate Hedstrom
@item Erik Schnetter
+@item Joost VandeVondele
@end itemize
Many other individuals have helped debug,
@item Bug hunting/squishing
Find bugs and write more test cases! Test cases are especially very
welcome, because it allows us to concentrate on fixing bugs instead of
-isolating them. Going through the bugzilla database at
-@url{http://gcc.gnu.org/bugzilla/} to reduce testcases posted there and
+isolating them. Going through the bugzilla database at
+@url{https://gcc.gnu.org/@/bugzilla/} to reduce testcases posted there and
add more information (for example, for which version does the testcase
work, for which versions does it fail?) is also very helpful.
existing Fortran compilers, but they are not part of the official
J3 Fortran 95 standard.
-@subsection Compiler extensions:
+@subsection Compiler extensions:
@itemize @bullet
@item
User-specified alignment rules for structures.
-@item
-Flag to generate @code{Makefile} info.
-
@item
Automatically extend single precision constants to double.
Environment variable for temporary file directory.
@item
-Environment variable forcing standard output to be line buffered (unix).
+Environment variable forcing standard output to be line buffered (Unix).
@end itemize
@node Option Index
@unnumbered Option Index
@command{gfortran}'s command line options are indexed here without any
-initial @samp{-} or @samp{--}. Where an option has both positive and
+initial @samp{-} or @samp{--}. Where an option has both positive and
negative forms (such as -foption and -fno-option), relevant entries in
the manual are indexed under the most appropriate form; it may sometimes
be useful to look up both forms.
projects / gcc.git / blobdiff