regex_executor.h

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// class template regex -*- C++ -*-
 
// Copyright (C) 2013-2026 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
 
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
 
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
 
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.
 
/**
 *  @file bits/regex_executor.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{regex}
 */
 
// FIXME convert comments to doxygen format.
 
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
 
namespace __detail
{
  /**
   * @addtogroup regex-detail
   * @{
   */
 
  template<typename _BiIter, bool _Trivial = is_trivially_copyable<_BiIter>::value>
    struct _ExecutorFrame;
 
_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
  /**
   * @brief Takes a regex and an input string and does the matching.
   *
   * The %_Executor class has two modes: DFS mode and BFS mode, controlled
   * by the function parameter %__search_mode.
   */
  enum class _Search_mode : unsigned char { _Bfs = 0, _Dfs = 1 };
 
  template<typename _BiIter, typename _Alloc, typename _TraitsT>
    class _Executor
    {
      enum class _Match_mode : unsigned char { _Exact, _Prefix };
 
    public:
      typedef typename iterator_traits<_BiIter>::value_type _CharT;
      typedef basic_regex<_CharT, _TraitsT>                 _RegexT;
      typedef _GLIBCXX_STD_C::vector<sub_match<_BiIter>, _Alloc> _ResultsVec;
      typedef regex_constants::match_flag_type              _FlagT;
      typedef typename _TraitsT::char_class_type            _ClassT;
      typedef _NFA<_TraitsT>                                _NFAT;
 
    public:
      _Executor(_BiIter         __begin,
                _BiIter         __end,
                _ResultsVec&    __results,
                const _RegexT&  __re,
                _FlagT          __flags,
                bool            __use_dfs)
      : _M_cur_results(__results.get_allocator()),
        _M_begin(__begin),
        _M_end(__end),
        _M_re(__re),
        _M_nfa(*__re._M_automaton),
        _M_results(__results),
        _M_rep_count(_M_nfa.size()),
        _M_start(_M_nfa._M_start()),
        _M_visited_states(nullptr),
        _M_flags(__flags),
        _M_search_mode(__use_dfs ? _Search_mode::_Dfs : _Search_mode::_Bfs)
      {
        using namespace regex_constants;
        if (__flags & match_prev_avail) // ignore not_bol and not_bow
          _M_flags &= ~(match_not_bol | match_not_bow);
        if (_M_search_mode == _Search_mode::_Bfs)
          _M_visited_states = new bool[_M_nfa.size()];
      }
 
      ~_Executor()
      { delete[] _M_visited_states; }
 
      // Set matched when string exactly matches the pattern.
      bool
      _M_match()
      {
        _M_current = _M_begin;
        return _M_main(_Match_mode::_Exact);
      }
 
      // Set matched when some prefix of the string matches the pattern.
      bool
      _M_search_from_first()
      {
        _M_current = _M_begin;
        // Fast reject for DFS prefix search.  regex_search and
        // regex_token_iterator try the pattern at each possible starting
        // position.  If the regex can only start with a digit, running the full
        // DFS executor at a space, letter, or punctuation character only builds
        // frames to discover the first match state rejects that character.
        //
        // Example: for the IPv4 pattern
        //   (?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9])\.){3}...
        // a current input character of 'x' cannot match any first consuming
        // state.  _M_maybe_start_match returns false and this starting position
        // is skipped.  At '2' it returns true, because at least one branch
        // might match, so the normal executor still decides the complete
        // result.
        //
        // This is intentionally disabled for backreferences.  Pruning the
        // search space for DFS reduces the number of frames we build and the
        // time to find an actual match.
        if (_M_search_mode == _Search_mode::_Dfs
            && !_M_nfa._M_has_backref
            && _M_current != _M_end
            && !_M_maybe_start_match(_M_start, 0))
          return false;
        return _M_main(_Match_mode::_Prefix);
      }
 
      bool
      _M_search();
 
    private:
      _StateIdT
      _M_rep_once_more(_Match_mode __match_mode, _StateIdT);
 
      _StateIdT
      _M_match_simple_repeat_body(_StateIdT, _StateIdT);
 
      template<_Search_mode __search_mode>
      _StateIdT
      _M_handle_repeat(_Match_mode, _StateIdT);
 
      template<_Search_mode __search_mode>
        _StateIdT
      _M_handle_subexpr_begin(_Match_mode, _StateIdT);
 
      template<_Search_mode __search_mode>
        _StateIdT
      _M_handle_subexpr_end(_Match_mode, _StateIdT);
 
      _StateIdT
      _M_handle_line_begin_assertion(_Match_mode, _StateIdT);
 
      _StateIdT
      _M_handle_line_end_assertion(_Match_mode, _StateIdT);
 
      _StateIdT
      _M_handle_word_boundary(_Match_mode, _StateIdT);
 
      _StateIdT
      _M_handle_subexpr_lookahead(_Match_mode, _StateIdT);
 
      template<_Search_mode __search_mode>
        _StateIdT
      _M_handle_match(_Match_mode, _StateIdT);
 
      _StateIdT
      _M_handle_backref(_Match_mode, _StateIdT);
 
      template<_Search_mode __search_mode>
        _StateIdT
      _M_handle_accept(_Match_mode, _StateIdT);
 
      _StateIdT
      _M_handle_alternative(_Match_mode, _StateIdT);
 
      template<_Search_mode __search_mode>
        _StateIdT
      _M_node(_Match_mode, _StateIdT);
 
      template<_Search_mode __search_mode>
        void
      _M_dfs(_Match_mode __match_mode, _StateIdT __start);
 
      bool
      _M_main(_Match_mode __match_mode)
      {
        if (_M_search_mode == _Search_mode::_Dfs)
          return _M_main_dfs(__match_mode);
        else
          return _M_main_bfs(__match_mode);
      }
 
      bool
      _M_main_dfs(_Match_mode __match_mode);
 
      bool
      _M_maybe_start_match(_StateIdT, size_t);
 
      bool
      _M_main_bfs(_Match_mode __match_mode);
 
      bool
      _M_is_word(_CharT __ch) const
      {
        static const _CharT __s[2] = { 'w' };
        return _M_re._M_automaton->_M_traits.isctype
          (__ch, _M_re._M_automaton->_M_traits.lookup_classname(__s, __s+1));
      }
 
      bool
      _M_at_begin() const
      {
        if (_M_current == _M_begin)
          {
            // match_not_bol means ^ does not match [_M_begin,_M_begin)
            if (_M_flags & regex_constants::match_not_bol)
              return false;
            // match_prev_avail means _M_begin is not the start of the input.
            if (_M_flags & regex_constants::match_prev_avail)
              {
                // For ECMAScript multiline matches, check if the previous
                // character is a line terminator.
                if (_M_match_multiline())
                  return _M_is_line_terminator(*std::prev(_M_current));
                else
                  return false;
              }
            else // ^ matches at _M_begin
              return true;
          }
        else if (_M_match_multiline())
          return _M_is_line_terminator(*std::prev(_M_current));
        else
          return false;
      }
 
      bool
      _M_at_end() const
      {
        if (_M_current == _M_end)
          return !(_M_flags & regex_constants::match_not_eol);
        else if (_M_match_multiline())
          return _M_is_line_terminator(*_M_current);
        else
          return false;
      }
 
      bool
      _M_word_boundary() const;
 
      bool
      _M_lookahead(_StateIdT __next);
 
      bool
      _M_is_line_terminator(_CharT __c) const
      {
        const auto& __traits = _M_re._M_automaton->_M_traits;
        const auto& __ct = use_facet<ctype<_CharT>>(__traits.getloc());
        const char __n{ __ct.narrow(__c, ' ') };
        if (__n == '\n')
          return true;
        if (_M_re._M_automaton->_M_options() & regex_constants::ECMAScript)
          {
            if (__n == '\r')
              return true;
            // FIXME: U+2028 (line separator) and U+2029 (paragraph separator)
          }
        return false;
      }
 
      bool
      _M_match_multiline() const noexcept
      {
        constexpr auto __m
          = regex_constants::ECMAScript | regex_constants::__multiline;
        return (_M_re._M_automaton->_M_options() & __m) == __m;
      }
 
      inline bool
      _M_visited(_StateIdT __i)
      {
        if (_M_visited_states)
          {
            if (_M_visited_states[__i])
              return true;
            _M_visited_states[__i] = true;
          }
        return false;
      }
 
      _BiIter* _M_get_sol_pos() { return &_M_sol_pos; }
 
    public:
      _GLIBCXX_STD_C::vector<_ExecutorFrame<_BiIter>>       _M_frames;
      _ResultsVec                                           _M_cur_results;
      _BiIter                                               _M_current;
      _BiIter                                               _M_begin;
      const _BiIter                                         _M_end;
      const _RegexT&                                        _M_re;
      const _NFAT&                                          _M_nfa;
      _ResultsVec&                                          _M_results;
      _GLIBCXX_STD_C::vector<pair<_BiIter, int>>            _M_rep_count;
      // To record current solution.
      _StateIdT                                             _M_start;
      _BiIter                                               _M_sol_pos;
      // (BFS only) Saves states that need to be considered for the next character.
      _GLIBCXX_STD_C::vector<pair<_StateIdT, _ResultsVec>>  _M_match_queue;
      // (BFS only) Indicates which states are already visited.
      bool*                                                 _M_visited_states;
      _FlagT                                                _M_flags;
      const _Search_mode                                    _M_search_mode;
      // Do we have a solution so far?
      bool                                                  _M_has_sol;
    };
_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
 
 ///@} regex-detail
} // namespace __detail
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
 
#include <bits/regex_executor.tcc>