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