* Conditionals:: Omitting the middle operand of a @samp{?:} expression.
* Long Long:: Double-word integers---@code{long long int}.
* Complex:: Data types for complex numbers.
-* Decimal Float:: Decimal Floating Point.
+* Decimal Float:: Decimal Floating Point.
* Hex Floats:: Hexadecimal floating-point constants.
* Zero Length:: Zero-length arrays.
* Variable Length:: Arrays whose length is computed at run time.
by a constructor. In this case, the static initialization and destruction
code for the object is emitted in each translation defining the object,
but the calls to the constructor and destructor are protected by a
-link-once guard variable.
+link-once guard variable.
The @code{selectany} attribute is only available on Microsoft Windows
targets. You can use @code{__declspec (selectany)} as a synonym for
Currently @option{-m[no-]ms-bitfields} is provided for the Microsoft Windows X86
compilers to match the native Microsoft compiler.
+
+The Microsoft structure layout algorithm is fairly simple with the exception
+of the bitfield packing:
+
+The padding and alignment of members of structures and whether a bit field
+can straddle a storage-unit boundary
+
+@enumerate
+@item Structure members are stored sequentially in the order in which they are
+declared: the first member has the lowest memory address and the last member
+the highest.
+
+@item Every data object has an alignment-requirement. The alignment-requirement
+for all data except structures, unions, and arrays is either the size of the
+object or the current packing size (specified with either the aligned attribute
+or the pack pragma), whichever is less. For structures, unions, and arrays,
+the alignment-requirement is the largest alignment-requirement of its members.
+Every object is allocated an offset so that:
+
+offset % alignment-requirement == 0
+
+@item Adjacent bit fields are packed into the same 1-, 2-, or 4-byte allocation
+unit if the integral types are the same size and if the next bit field fits
+into the current allocation unit without crossing the boundary imposed by the
+common alignment requirements of the bit fields.
+@end enumerate
+
+Handling of zero-length bitfields:
+
+MSVC interprets zero-length bitfields in the following ways:
+
+@enumerate
+@item If a zero-length bitfield is inserted between two bitfields that would
+normally be coalesced, the bitfields will not be coalesced.
+
+For example:
+
+@smallexample
+struct
+ @{
+ unsigned long bf_1 : 12;
+ unsigned long : 0;
+ unsigned long bf_2 : 12;
+ @} t1;
+@end smallexample
+
+The size of @code{t1} would be 8 bytes with the zero-length bitfield. If the
+zero-length bitfield were removed, @code{t1}'s size would be 4 bytes.
+
+@item If a zero-length bitfield is inserted after a bitfield, @code{foo}, and the
+alignment of the zero-length bitfield is greater than the member that follows it,
+@code{bar}, @code{bar} will be aligned as the type of the zero-length bitfield.
+
+For example:
+
+@smallexample
+struct
+ @{
+ char foo : 4;
+ short : 0;
+ char bar;
+ @} t2;
+
+struct
+ @{
+ char foo : 4;
+ short : 0;
+ double bar;
+ @} t3;
+@end smallexample
+
+For @code{t2}, @code{bar} will be placed at offset 2, rather than offset 1.
+Accordingly, the size of @code{t2} will be 4. For @code{t3}, the zero-length
+bitfield will not affect the alignment of @code{bar} or, as a result, the size
+of the structure.
+
+Taking this into account, it is important to note the following:
+
+@enumerate
+@item If a zero-length bitfield follows a normal bitfield, the type of the
+zero-length bitfield may affect the alignment of the structure as whole. For
+example, @code{t2} has a size of 4 bytes, since the zero-length bitfield follows a
+normal bitfield, and is of type short.
+
+@item Even if a zero-length bitfield is not followed by a normal bitfield, it may
+still affect the alignment of the structure:
+
+@smallexample
+struct
+ @{
+ char foo : 6;
+ long : 0;
+ @} t4;
+@end smallexample
+
+Here, @code{t4} will take up 4 bytes.
+@end enumerate
+
+@item Zero-length bitfields following non-bitfield members are ignored:
+
+@smallexample
+struct
+ @{
+ char foo;
+ long : 0;
+ char bar;
+ @} t5;
+@end smallexample
+
+Here, @code{t5} will take up 2 bytes.
+@end enumerate
@end table
@subsection Xstormy16 Variable Attributes
value of @code{*@var{ptr}} is @var{oldval}, then write @var{newval} into
@code{*@var{ptr}}.
-The ``bool'' version returns true if the comparison is successful and
+The ``bool'' version returns true if the comparison is successful and
@var{newval} was written. The ``val'' version returns the contents
of @code{*@var{ptr}} before the operation.
This builtin is not a full barrier, but rather an @dfn{acquire barrier}.
This means that references after the builtin cannot move to (or be
speculated to) before the builtin, but previous memory stores may not
-be globally visible yet, and previous memory loads may not yet be
+be globally visible yet, and previous memory loads may not yet be
satisfied.
@item void __sync_lock_release (@var{type} *ptr, ...)
v2si __builtin_ia32_pswapdsi (v2si)
@end smallexample
-The following built-in functions are available when @option{-msse2}
-is used. All of them generate calls to an SSE2 ABI IEEE754 math intrinsic
-that is part of the name. Rather than using these directly you may
-want them automatically substituted for calls to the regular intrinsics
-using the @option{-msselibm}.
-
-@smallexample
-double __builtin_sse2_acos (double)
-float __builtin_sse2_acosf (float)
-double __builtin_sse2_asin (double)
-float __builtin_sse2_asinf (float)
-double __builtin_sse2_atan (double)
-float __builtin_sse2_atanf (float)
-double __builtin_sse2_atan2 (double, double)
-float __builtin_sse2_atan2f (float, float)
-double __builtin_sse2_cos (double)
-float __builtin_sse2_cosf (float)
-double __builtin_sse2_exp (double)
-float __builtin_sse2_expf (float)
-double __builtin_sse2_log10 (double)
-float __builtin_sse2_log10f (float)
-double __builtin_sse2_log (double)
-float __builtin_sse2_logf (float)
-double __builtin_sse2_sin (double)
-float __builtin_sse2_sinf (float)
-double __builtin_sse2_tan (double)
-float __builtin_sse2_tanf (float)
-@end smallexample
-
@node MIPS DSP Built-in Functions
@subsection MIPS DSP Built-in Functions
@cindex pragma, weak
This pragma declares @var{symbol} to be weak, as if the declaration
had the attribute of the same name. The pragma may appear before
-or after the declaration of @var{symbol}, but must appear before
+or after the declaration of @var{symbol}, but must appear before
either its first use or its definition. It is not an error for
@var{symbol} to never be defined at all.
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