libstdc++-v3/include/bits/regex_automaton.h

// 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_automaton.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{regex}
 */

// This macro defines the maximal state number a NFA can have.
#ifndef _GLIBCXX_REGEX_STATE_LIMIT
#define _GLIBCXX_REGEX_STATE_LIMIT 100000
#endif

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpedantic" // anon struct

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

namespace __detail
{
  /**
   *  @defgroup regex-detail Base and Implementation Classes
   *  @ingroup regex
   *  @{
   */

  typedef long _StateIdT;
  _GLIBCXX17_INLINE constexpr _StateIdT _S_invalid_state_id  = -1;

  template<typename _CharT>
    using _Matcher = std::function<bool (_CharT)>;

  /// Operation codes that define the type of transitions within the base NFA
  /// that represents the regular expression.
  enum _Opcode : int
  {
      _S_opcode_unknown,
      _S_opcode_alternative,
      _S_opcode_repeat,
      _S_opcode_backref,
      _S_opcode_line_begin_assertion,
      _S_opcode_line_end_assertion,
      _S_opcode_word_boundary,
      _S_opcode_subexpr_lookahead,
      _S_opcode_subexpr_begin,
      _S_opcode_subexpr_end,
      _S_opcode_dummy,
      _S_opcode_match,
      _S_opcode_accept,
  };

  struct _State_base
  {
  protected:
    _Opcode      _M_opcode;           // type of outgoing transition

  public:
    _StateIdT    _M_next;             // outgoing transition
    union // Since they are mutually exclusive.
    {
      size_t _M_subexpr;        // for _S_opcode_subexpr_*
      size_t _M_backref_index;  // for _S_opcode_backref
      struct
      {
	// for _S_opcode_alternative, _S_opcode_repeat and
	// _S_opcode_subexpr_lookahead
	_StateIdT  _M_alt;
	// for _S_opcode_word_boundary or _S_opcode_subexpr_lookahead or
	// quantifiers (ungreedy if set true)
	bool       _M_neg;
      };
      // For _S_opcode_match
      __gnu_cxx::__aligned_membuf<_Matcher<char>> _M_matcher_storage;
    };

  protected:
    explicit _State_base(_Opcode __opcode) noexcept
    : _M_opcode(__opcode), _M_next(_S_invalid_state_id)
    { }

  public:
    bool
    _M_has_alt() const noexcept
    {
      return _M_opcode == _S_opcode_alternative
	|| _M_opcode == _S_opcode_repeat
	|| _M_opcode == _S_opcode_subexpr_lookahead;
    }

#ifdef _GLIBCXX_DEBUG
    std::ostream&
    _M_print(std::ostream& __ostr) const;

    // Prints graphviz dot commands for state.
    std::ostream&
    _M_dot(std::ostream& __ostr, _StateIdT __id) const;
#endif
  };

  template<typename _Char_type>
    struct _State : _State_base
    {
      typedef _Matcher<_Char_type> _MatcherT;
      static_assert(sizeof(_MatcherT) == sizeof(_Matcher<char>),
		    "std::function<bool(T)> has the same size as "
		    "std::function<bool(char)>");
      static_assert(alignof(_MatcherT) == alignof(_Matcher<char>),
		    "std::function<bool(T)> has the same alignment as "
		    "std::function<bool(char)>");

      explicit
      _State(_Opcode __opcode) noexcept : _State_base(__opcode)
      {
	if (_M_opcode() == _S_opcode_match)
	  new (this->_M_matcher_storage._M_addr()) _MatcherT();
      }

      _State(const _State& __rhs) : _State_base(__rhs)
      {
	if (__rhs._M_opcode() == _S_opcode_match)
	  new (this->_M_matcher_storage._M_addr())
	    _MatcherT(__rhs._M_get_matcher());
      }

      _State(_State&& __rhs) noexcept : _State_base(__rhs)
      {
	if (__rhs._M_opcode() == _S_opcode_match)
	  new (this->_M_matcher_storage._M_addr())
	    _MatcherT(std::move(__rhs._M_get_matcher()));
      }

      _State&
      operator=(const _State&) = delete;

      ~_State()
      {
	if (_M_opcode() == _S_opcode_match)
	  _M_get_matcher().~_MatcherT();
      }

      // Since correct ctor and dtor rely on _M_opcode, it's better not to
      // change it over time.
      _Opcode
      _M_opcode() const noexcept
      { return _State_base::_M_opcode; }

      bool
      _M_matches(_Char_type __char) const
      { return _M_get_matcher()(__char); }

      _MatcherT&
      _M_get_matcher() noexcept
      { return *static_cast<_MatcherT*>(this->_M_matcher_storage._M_addr()); }

      const _MatcherT&
      _M_get_matcher() const noexcept
      {
	return *static_cast<const _MatcherT*>(
	    this->_M_matcher_storage._M_addr());
      }
    };

  struct _NFA_base
  {
    typedef regex_constants::syntax_option_type _FlagT;

    explicit
    _NFA_base(_FlagT __f) noexcept
    : _M_flags(__f), _M_start_state(0), _M_subexpr_count(0),
    _M_has_backref(false)
    { }

    _NFA_base(_NFA_base&&) = default;

  protected:
    ~_NFA_base() = default;

  public:
    _FlagT
    _M_options() const noexcept
    { return _M_flags; }

    _StateIdT
    _M_start() const noexcept
    { return _M_start_state; }

    size_t
    _M_sub_count() const noexcept
    { return _M_subexpr_count; }

    _GLIBCXX_STD_C::vector<size_t> _M_paren_stack;
    _FlagT                    _M_flags;
    _StateIdT                 _M_start_state;
    size_t                    _M_subexpr_count;
    bool                      _M_has_backref;
  };

  template<typename _TraitsT>
    struct _NFA
    : _NFA_base, _GLIBCXX_STD_C::vector<_State<typename _TraitsT::char_type>>
    {
      typedef typename _TraitsT::char_type	_Char_type;
      typedef _State<_Char_type>		_StateT;
      typedef _Matcher<_Char_type>		_MatcherT;

      _NFA(const typename _TraitsT::locale_type& __loc, _FlagT __flags)
      : _NFA_base(__flags)
      { _M_traits.imbue(__loc); }

      // for performance reasons _NFA objects should only be moved not copied
      _NFA(const _NFA&) = delete;
      _NFA(_NFA&&) = default;

      _StateIdT
      _M_insert_accept()
      {
	auto __ret = _M_insert_state(_StateT(_S_opcode_accept));
	return __ret;
      }

      _StateIdT
      _M_insert_alt(_StateIdT __next, _StateIdT __alt,
		    bool __neg __attribute__((__unused__)))
      {
	_StateT __tmp(_S_opcode_alternative);
	// It labels every quantifier to make greedy comparison easier in BFS
	// approach.
	__tmp._M_next = __next;
	__tmp._M_alt = __alt;
	return _M_insert_state(std::move(__tmp));
      }

      _StateIdT
      _M_insert_repeat(_StateIdT __next, _StateIdT __alt, bool __neg)
      {
	_StateT __tmp(_S_opcode_repeat);
	// It labels every quantifier to make greedy comparison easier in BFS
	// approach.
	__tmp._M_next = __next;
	__tmp._M_alt = __alt;
	__tmp._M_neg = __neg;
	return _M_insert_state(std::move(__tmp));
      }

      _StateIdT
      _M_insert_matcher(_MatcherT __m)
      {
	_StateT __tmp(_S_opcode_match);
	__tmp._M_get_matcher() = std::move(__m);
	return _M_insert_state(std::move(__tmp));
      }

      _StateIdT
      _M_insert_subexpr_begin()
      {
	auto __id = this->_M_subexpr_count++;
	this->_M_paren_stack.push_back(__id);
	_StateT __tmp(_S_opcode_subexpr_begin);
	__tmp._M_subexpr = __id;
	return _M_insert_state(std::move(__tmp));
      }

      _StateIdT
      _M_insert_subexpr_end()
      {
	_StateT __tmp(_S_opcode_subexpr_end);
	__tmp._M_subexpr = this->_M_paren_stack.back();
	this->_M_paren_stack.pop_back();
	return _M_insert_state(std::move(__tmp));
      }

      _StateIdT
      _M_insert_backref(size_t __index);

      _StateIdT
      _M_insert_line_begin()
      { return _M_insert_state(_StateT(_S_opcode_line_begin_assertion)); }

      _StateIdT
      _M_insert_line_end()
      { return _M_insert_state(_StateT(_S_opcode_line_end_assertion)); }

      _StateIdT
      _M_insert_word_bound(bool __neg)
      {
	_StateT __tmp(_S_opcode_word_boundary);
	__tmp._M_neg = __neg;
	return _M_insert_state(std::move(__tmp));
      }

      _StateIdT
      _M_insert_lookahead(_StateIdT __alt, bool __neg)
      {
	_StateT __tmp(_S_opcode_subexpr_lookahead);
	__tmp._M_alt = __alt;
	__tmp._M_neg = __neg;
	return _M_insert_state(std::move(__tmp));
      }

      _StateIdT
      _M_insert_dummy()
      { return _M_insert_state(_StateT(_S_opcode_dummy)); }

      _StateIdT
      _M_insert_state(_StateT __s)
      {
	this->push_back(std::move(__s));
	if (this->size() > _GLIBCXX_REGEX_STATE_LIMIT)
	  __throw_regex_error(
	    regex_constants::error_space,
	    "Number of NFA states exceeds limit. Please use shorter regex "
	    "string, or use smaller brace expression, or make "
	    "_GLIBCXX_REGEX_STATE_LIMIT larger.");
	return this->size() - 1;
      }

      // Eliminate dummy node in this NFA to make it compact.
      void
      _M_eliminate_dummy();

#ifdef _GLIBCXX_DEBUG
      std::ostream&
      _M_dot(std::ostream& __ostr) const;
#endif
    public:
      _TraitsT                  _M_traits;
    };

  /// Describes a sequence of one or more %_State, its current start
  /// and end(s).  This structure contains fragments of an NFA during
  /// construction.
  template<typename _TraitsT>
    class _StateSeq
    {
    public:
      typedef _NFA<_TraitsT> _RegexT;

    public:
      _StateSeq(_RegexT& __nfa, _StateIdT __s)
      : _M_nfa(__nfa), _M_start(__s), _M_end(__s)
      { }

      _StateSeq(_RegexT& __nfa, _StateIdT __s, _StateIdT __end)
      : _M_nfa(__nfa), _M_start(__s), _M_end(__end)
      { }

      // Append a state on *this and change *this to the new sequence.
      void
      _M_append(_StateIdT __id)
      {
	_M_nfa[_M_end]._M_next = __id;
	_M_end = __id;
      }

      // Append a sequence on *this and change *this to the new sequence.
      void
      _M_append(const _StateSeq& __s)
      {
	_M_nfa[_M_end]._M_next = __s._M_start;
	_M_end = __s._M_end;
      }

      // Clones an entire sequence.
      _StateSeq
      _M_clone();

    public:
      _RegexT&  _M_nfa;
      _StateIdT _M_start;
      _StateIdT _M_end;
    };

 ///@} regex-detail
} // namespace __detail

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#pragma GCC diagnostic pop

#include <bits/regex_automaton.tcc>