NEWS

   1 This file contains a summary of important user-visible changes.
   2
   3 Changes since 1.8
   4 =================
   5
   6 New Features:
   7 * A new parametric theory of sequences whose syntax is compatible with the
   8   syntax for sequences used by Z3.
   9 * Arrays: Added support for an `eqrange` predicate. `(eqrange a b i j)` is true
  10   if arrays `a` and `b` are equal on all indices within indices `i` and `j`.
  11 * Support for an integer operator `(_ iand n)` that returns the bitwise `and`
  12   of two integers, seen as integers modulo n.
  13
  14 Improvements:
  15 * New API: Added functions to retrieve the heap/nil term when using separation
  16   logic.
  17
  18 Changes:
  19 * SyGuS: Removed support for SyGuS-IF 1.0.
  20 * Removed Java and Python bindings for the legacy API
  21 * Interactive shell: the GPL-licensed Readline library has been replaced the
  22   BSD-licensed Editline. Compiling with `--best` now enables Editline, instead
  23   of Readline. Without selecting optional GPL components, Editline-enabled CVC4
  24   builds will be BSD licensed.
  25 * The semantics for division and remainder operators in the CVC language now
  26   correspond to SMT-LIB 2.6 semantics (i.e. a division by zero or a zero
  27   modulus results in a constant value, instead of an uninterpreted one).
  28   Similarly, when no language is set, the API semantics now correspond to the
  29   SMT-LIB 2.6 semantics.
  30 * The `competition` build type includes the dependencies used for SMT-COMP by
  31   default. Note that this makes this build type produce GPL-licensed binaries.
  32 * Bit-vector operator bvxnor was previously mistakenly marked as
  33   left-assoicative in SMT-LIB. This has recently been corrected in SMT-LIB. We
  34   now restrict bvxnor to only allow two operands in order to avoid confusion
  35   about the semantics, since the behavior of n-ary operands to bvxnor is now
  36   undefined in SMT-LIB.
  37 * SMT-LIB output for `get-model` command now conforms with the standard,
  38   and does *not* begin with the keyword `model`. The output
  39   is the same as before, only with this word removed from the beginning.
  40 * Building with Python 2 is now deprecated.
  41
  42
  43 Changes since 1.7
  44 =================
  45
  46 New Features:
  47 * New C++ and Python API: CVC4 has a new, more streamlined API. We plan to
  48   make CVC4 1.8 the last version that ships with the legacy API.
  49 * Strings: Full support of the new SMT-LIB standard for the theory of strings,
  50   including:
  51   * Support for `str.replace_re`, `str.replace_re_all`, `str.is_digit`,
  52     `str.from_code`, `re.diff`, and `re.comp`
  53   * Support for new operator names (e.g. `str.in_re` instead of `str.in.re`),
  54     new escape sequences. The new syntax is enabled by default for smt2 files.
  55 * Support for syntax-guided synthesis (SyGuS) problems in the new API. C++
  56   examples of the SyGuS API can be found in `./examples/api/sygus_*.cpp`.
  57 * Support for higher-order constraints. This includes treating function sorts
  58   (constructible by `->`) as first-class sorts and handling partially applied
  59   function symbols. Support for higher-order constraints can be enabled by
  60   the option `--uf-ho`.
  61 * Support for set comprehension binders `comprehension`.
  62 * Eager bit-blasting: Support for SAT solver Kissat.
  63
  64 Improvements:
  65 * API: Function definitions can now be requested to be global. If the `global`
  66   parameter is set to true, they persist after popping the user context.
  67 * Java/Python bindings: The bindings now allow users to catch exceptions
  68 * Arithmetic: Performance improvements
  69   * Linear solver: New lemmas inspired by unit-cube tests
  70   * Non-linear solver: Expanded set of axioms
  71 * Ackermannization: The Ackermannization preprocessing pass now supports
  72   uninterpreted sorts and as a result all QF_UFBV problems are supported in
  73   combination with eager bit blasting.
  74
  75 Changes:
  76 * CVC language: Models printed in the CVC language now include an explicit end
  77   marker to facilitate the communication over pipes with CVC4.
  78 * API change: `SmtEngine::query()` has been renamed to
  79   `SmtEngine::checkEntailed()` and `Result::Validity` has been renamed to
  80   `Result::Entailment` along with corresponding changes to the enum values.
  81 * Java API change: The name of CVC4's package is now `edu.stanford.CVC4`
  82   instead of `edu.nyu.acsys.CVC4`.
  83 * The default output language is changed from CVC to SMT-LIB 2.6. The
  84   default output language is used when the problem language cannot be
  85   easily inferred (for example when CVC4 is used from the API).
  86 * Printing of BV constants: previously CVC4 would print BV constant
  87   values as indexed symbols by default and in binary notation with the
  88   option --bv-print-consts-in-binary. To be SMT-LIB compliant the
  89   default behavior is now to print BV constant values in binary
  90   notation and as indexed symbols with the new option
  91   --bv-print-consts-as-indexed-symbols. The option
  92   --bv-print-consts-in-binary has been removed.
  93 * Updated to SyGuS language version 2.0 by default. This is the last release
  94   that will support the SyGuS language version 1.0 (`--lang=sygus1`). A
  95   script is provided to convert version 1.0 files to version 2.0, see
  96   `./contrib/sygus-v1-to-v2.sh`.
  97 * Support for user-provided rewrite rule quantifiers have been removed.
  98 * Support for certain option aliases have been removed.
  99 * Support for parallel portfolio builds has been removed.
 100
 101 Changes since 1.6
 102 =================
 103
 104 New Features:
 105 * Proofs:
 106   * Support for bit-vector proofs with eager bitblasting (older versions only
 107     supported proofs with lazy bitblasting).
 108 * Strings:
 109   * Support for `str.replaceall` operator.
 110   * New option `--re-elim` to reduce regular expressions to extended string
 111     operators, resulting in better performance on regular expression benchmarks
 112     (enabled by default).
 113 * SyGuS:
 114   * Support for abduction (`--sygus-abduct`). Given a formula, this option uses
 115     CVC4's SyGuS solver to find a sufficient condition such that the
 116     conjunction of the condition and the formula is unsatisfiable.
 117   * Support for two new term enumerator strategies: variable agnostic
 118     (`--sygus-active-gen=var-agnostic`) and fast (`--sygus-active-gen=enum`).
 119     By default, CVC4 tries to choose the best term enumerator strategy
 120     automatically based on the input (`--sygus-active-gen=auto`).
 121   * Support for streaming solutions of increasingly smaller size when using the
 122     PBE solver (`--sygus-stream --sygus-pbe`). After the first solution is found
 123     and printed, the solver will continue to look for new solutions and print
 124     those, if any, that are smaller than previously printed solutions.
 125   * Support for unification-based techniques in non-separable specifications
 126     (`--sygus-unif`). For solving invariant problems a dedicate mode
 127     (`--sygus-unif-boolean-heuristic-dt`) is available that builds candidate
 128     solutions using heuristic decision tree learning.
 129
 130 Improvements:
 131 * Strings:
 132   * Significantly better performance on string benchmarks over the core theory
 133     and those with extended string functions like substring, contains, and
 134     replace.
 135
 136 Changes:
 137 * API change: Expr::iffExpr() is renamed to Expr::eqExpr() to reflect its
 138               actual behavior.
 139 * Compiling the language bindings now requires SWIG 3 instead of SWIG 2.
 140 * The CVC3 compatibility layer has been removed.
 141 * The build system now uses CMake instead of Autotools. Please refer to
 142   [INSTALL.md](https://github.com/CVC4/CVC4/blob/master/INSTALL.md) for
 143   up-to-date instructions on how to build CVC4.
 144
 145 Changes since 1.5
 146 =================
 147
 148 New Features:
 149 * A new theory of floating points.
 150 * Novel approach for solving quantified bit-vectors (BV).
 151 * Eager bit-blasting: Support for SAT solver CaDiCaL.
 152 * A new Gaussian Elimination preprocessing pass for the theory of bit-vectors.
 153 * Support for transcendental functions (sin, cos, exp). In SMT2 input, this
 154   can be enabled by adding T to the logic (e.g., QF_NRAT).
 155 * Support for new operators in strings, including string inequality (str.<=)
 156   and string code (str.code).
 157 * Support for automated rewrite rule generation from sygus (*.sy) inputs using
 158   syntax-guided enumeration (option --sygus-rr).
 159
 160 Improvements:
 161 * Incremental unsat core support.
 162 * Further development of rewrite rules for the theory of strings and regular
 163   expressions.
 164 * Many optimizations for syntax-guided synthesis, including improved symmetry
 165   breaking for enumerative search and specialized algorithms for
 166   programming-by-examples conjectures.
 167
 168 Changes:
 169 * Eager bit-blasting: Removed support for SAT solver CryptoMinisat 4, added
 170   support for CryptoMinisat 5.
 171 * The LFSC proof checker now resides in its own repository on GitHub at
 172   https://github.com/CVC4/LFSC. It is not distributed with CVC4 anymore.
 173
 174 Changes since 1.4
 175 =================
 176
 177 * Improved heuristics for reasoning about non-linear arithmetic.
 178 * Native support for syntax-guided synthesis (sygus).
 179 * Support for many new heuristics for reasoning with quantifiers, including
 180   finite model finding.
 181 * Support for proofs for uninterpreted functions, arrays, bitvectors, and
 182   their combinations.
 183 * Performance improvements to existing theories.
 184 * A new theory of sets with cardinality and relations.
 185 * A new theory of strings.
 186 * Support for unsat cores.
 187 * Support for separation logic constraints.
 188 * Simplification mode "incremental" no longer supported.
 189 * Support for array constants in constraints.
 190 * Syntax for array models has changed in some language front-ends.
 191 * New input/output languages supported: "smt2.0" and "smtlib2.0" to
 192   force SMT-LIB v2.0; "smt2.5" and "smtlib2.5" to force SMT-LIB v2.5;
 193   "smt2.6" and "smtlib2.6" to force SMT-LIB v2.6;
 194   "smt", "smtlib", "smt2", and "smtlib2" all refer to the current standard
 195   version 2.6.  If an :smt-lib-version is set in the input, that overrides
 196   the command line.
 197 * Abstract values in SMT-LIB models are now ascribed types (with "as").
 198 * In SMT-LIB model output, real-sorted but integer-valued constants are
 199   now printed in accordance with the standard (e.g. "1.0").
 200
 201 Changes since 1.3
 202 =================
 203
 204 * CVC4 now supports libc++ in addition to libstdc++ (this especially
 205   helps on Mac OS Mavericks).
 206 * The LFSC proof checker has been incorporated into CVC4 sources.
 207 * Theory of finite sets, handling the MLSS fragment (singleton, union,
 208   intersection, set subtraction, membership and subset).
 209 * By default, CVC4 builds in "production" mode (optimized, with fewer
 210   internal checks on).  The common alternative is a "debug" build, which
 211   is much slower.  By default, CVC4 builds with no GPL'ed dependences.
 212   However, this is not the best-performing version; for that, you should
 213   configure with "--enable-gpl --best", which links against GPL'ed
 214   libraries that improve usability and performance.  For details on
 215   licensing and dependences, see the README file.
 216 * Small API adjustments to Datatypes to even out the API and make it
 217   function better in Java.
 218 * Timed statistics are now properly updated even on process abort.
 219 * Better automatic handling of output language setting when using CVC4
 220   via API.  Previously, the "automatic" language setting was sometimes
 221   (though not always) defaulting to the internal "AST" language; it
 222   should now (correctly) default to the same as the input language
 223   (if the input language is supported as an output language), or the
 224   "CVC4" native output language if no input language setting is applied.
 225 * The SmtEngine cannot be safely copied with the copy constructor.
 226   Previous versions inadvertently permitted clients to do this via the
 227   API.  This has been corrected, copy and assignment of the SmtEngine
 228   is no longer permitted.
 229
 230 Changes since 1.2
 231 =================
 232
 233 New features:
 234 * SMT-LIB-compliant support for abs, to_real, to_int, is_int, which were
 235   previously missing
 236 * New bv2nat/int2bv operators for bitvector/integer inter-compatibility.
 237 * Support in linear logics for /, div, and mod by constants (with the
 238   --rewrite-divk command line option).
 239 * Parsing support for TPTP's TFF and TFA formats.
 240 * A new theory of strings: word (dis-)equations, length constraints,
 241   regular expressions.
 242 * Increased compliance to SMT-LIBv2, numerous bugs and usability issues
 243   resolved.
 244 * New :command-verbosity SMT option to silence success and error messages
 245   on a per-command basis, and API changes to Command infrastructure to
 246   support this.
 247
 248 Behavioral changes:
 249 * It is no longer permitted to request model or proof generation if there's
 250   been an intervening push/pop.
 251 * User-defined symbols (define-funs) are no longer reported in the output
 252   of get-model commands.
 253 * Exit codes are now more standard for UNIX command-line tools.  Exit code
 254   zero means no error---but the result could be sat, unsat, or unknown---and
 255   nonzero means error.
 256
 257 API changes:
 258 * Expr::substitute() now capable of substituting operators (e.g.,
 259   function symbols under an APPLY_UF)
 260 * Numerous improvements to the Java language bindings
 261
 262 Changes since 1.1
 263 =================
 264
 265 * Real arithmetic now has three simplex solvers for exact precision linear
 266   arithmetic: the classical dual solver and two new solvers based on
 267   techniques for minimizing the sum of infeasibilities. GLPK can now be used
 268   as a heuristic backup to the exact precision solvers.  GLPK must be enabled
 269   at configure time. See --help for more information on enabling these solvers.
 270 * added support for "bit0" and "bit1" bitvector constants in SMT-LIB v1.2
 271 * support for theory "alternates": new ability to prototype new decision
 272   procedures that are selectable at runtime
 273 * various bugfixes
 274
 275 Changes since 1.0
 276 =================
 277
 278 * bit-vector solver now has a specialized decision procedure for unsigned bit-
 279   vector inequalities
 280 * numerous important bug fixes, performance improvements, and usability
 281   improvements
 282 * support for multiline input in interactive mode
 283 * Win32-building support via mingw
 284 * SMT-LIB get-model output now is easier to machine-parse: contains (model...)
 285 * user patterns for quantifier instantiation are now supported in the
 286   SMT-LIBv1.2 parser
 287 * --finite-model-find was incomplete when using --incremental, now fixed
 288 * the E-matching procedure is slightly improved
 289 * Boolean terms are now supported in datatypes
 290 * tuple and record support have been added to the compatibility library
 291 * driver verbosity change: for printing all commands as they're executed, you
 292   now need verbosity level >= 3 (e.g., -vvv) instead of level 1 (-v).  This
 293   allows tracing the solver's activities (with -v and -vv) without having too
 294   much output.
 295 * to make CVC4 quieter in abnormal (e.g., "warning" conditions), you can
 296   use -q.  Previously, this would silence all output (including "sat" or
 297   "unsat") as well.  Now, single -q silences messages and warnings, and
 298   double -qq silences all output (except on exception or signal).