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- // class template regex -*- C++ -*-
- // Copyright (C) 2013-2022 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.tcc
- * This is an internal header file, included by other library headers.
- * Do not attempt to use it directly. @headername{regex}
- */
- namespace std _GLIBCXX_VISIBILITY(default)
- {
- _GLIBCXX_BEGIN_NAMESPACE_VERSION
- namespace __detail
- {
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_search()
- {
- if (_M_search_from_first())
- return true;
- if (_M_flags & regex_constants::match_continuous)
- return false;
- _M_flags |= regex_constants::match_prev_avail;
- while (_M_begin != _M_end)
- {
- ++_M_begin;
- if (_M_search_from_first())
- return true;
- }
- return false;
- }
- // The _M_main function operates in different modes, DFS mode or BFS mode,
- // indicated by template parameter __dfs_mode, and dispatches to one of the
- // _M_main_dispatch overloads.
- //
- // ------------------------------------------------------------
- //
- // DFS mode:
- //
- // It applies a Depth-First-Search (aka backtracking) on given NFA and input
- // string.
- // At the very beginning the executor stands in the start state, then it
- // tries every possible state transition in current state recursively. Some
- // state transitions consume input string, say, a single-char-matcher or a
- // back-reference matcher; some don't, like assertion or other anchor nodes.
- // When the input is exhausted and/or the current state is an accepting
- // state, the whole executor returns true.
- //
- // TODO: This approach is exponentially slow for certain input.
- // Try to compile the NFA to a DFA.
- //
- // Time complexity: \Omega(match_length), O(2^(_M_nfa.size()))
- // Space complexity: \theta(match_results.size() + match_length)
- //
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_main_dispatch(_Match_mode __match_mode, __dfs)
- {
- _M_has_sol = false;
- *_M_states._M_get_sol_pos() = _BiIter();
- _M_cur_results = _M_results;
- _M_dfs(__match_mode, _M_states._M_start);
- return _M_has_sol;
- }
- // ------------------------------------------------------------
- //
- // BFS mode:
- //
- // Russ Cox's article (http://swtch.com/~rsc/regexp/regexp1.html)
- // explained this algorithm clearly.
- //
- // It first computes epsilon closure (states that can be achieved without
- // consuming characters) for every state that's still matching,
- // using the same DFS algorithm, but doesn't re-enter states (using
- // _M_states._M_visited to check), nor follow _S_opcode_match.
- //
- // Then apply DFS using every _S_opcode_match (in _M_states._M_match_queue)
- // as the start state.
- //
- // It significantly reduces potential duplicate states, so has a better
- // upper bound; but it requires more overhead.
- //
- // Time complexity: \Omega(match_length * match_results.size())
- // O(match_length * _M_nfa.size() * match_results.size())
- // Space complexity: \Omega(_M_nfa.size() + match_results.size())
- // O(_M_nfa.size() * match_results.size())
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_main_dispatch(_Match_mode __match_mode, __bfs)
- {
- _M_states._M_queue(_M_states._M_start, _M_results);
- bool __ret = false;
- while (1)
- {
- _M_has_sol = false;
- if (_M_states._M_match_queue.empty())
- break;
- std::fill_n(_M_states._M_visited_states, _M_nfa.size(), false);
- auto __old_queue = std::move(_M_states._M_match_queue);
- for (auto& __task : __old_queue)
- {
- _M_cur_results = std::move(__task.second);
- _M_dfs(__match_mode, __task.first);
- }
- if (__match_mode == _Match_mode::_Prefix)
- __ret |= _M_has_sol;
- if (_M_current == _M_end)
- break;
- ++_M_current;
- }
- if (__match_mode == _Match_mode::_Exact)
- __ret = _M_has_sol;
- _M_states._M_match_queue.clear();
- return __ret;
- }
- // Return whether now match the given sub-NFA.
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_lookahead(_StateIdT __next)
- {
- // Backreferences may refer to captured content.
- // We may want to make this faster by not copying,
- // but let's not be clever prematurely.
- _ResultsVec __what(_M_cur_results);
- _Executor __sub(_M_current, _M_end, __what, _M_re, _M_flags);
- __sub._M_states._M_start = __next;
- if (__sub._M_search_from_first())
- {
- for (size_t __i = 0; __i < __what.size(); __i++)
- if (__what[__i].matched)
- _M_cur_results[__i] = __what[__i];
- return true;
- }
- return false;
- }
- // __rep_count records how many times (__rep_count.second)
- // this node is visited under certain input iterator
- // (__rep_count.first). This prevent the executor from entering
- // infinite loop by refusing to continue when it's already been
- // visited more than twice. It's `twice` instead of `once` because
- // we need to spare one more time for potential group capture.
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_rep_once_more(_Match_mode __match_mode, _StateIdT __i)
- {
- const auto& __state = _M_nfa[__i];
- auto& __rep_count = _M_rep_count[__i];
- if (__rep_count.second == 0 || __rep_count.first != _M_current)
- {
- auto __back = __rep_count;
- __rep_count.first = _M_current;
- __rep_count.second = 1;
- _M_dfs(__match_mode, __state._M_alt);
- __rep_count = __back;
- }
- else
- {
- if (__rep_count.second < 2)
- {
- __rep_count.second++;
- _M_dfs(__match_mode, __state._M_alt);
- __rep_count.second--;
- }
- }
- }
- // _M_alt branch is "match once more", while _M_next is "get me out
- // of this quantifier". Executing _M_next first or _M_alt first don't
- // mean the same thing, and we need to choose the correct order under
- // given greedy mode.
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_handle_repeat(_Match_mode __match_mode, _StateIdT __i)
- {
- const auto& __state = _M_nfa[__i];
- // Greedy.
- if (!__state._M_neg)
- {
- _M_rep_once_more(__match_mode, __i);
- // If it's DFS executor and already accepted, we're done.
- if (!__dfs_mode || !_M_has_sol)
- _M_dfs(__match_mode, __state._M_next);
- }
- else // Non-greedy mode
- {
- if (__dfs_mode)
- {
- // vice-versa.
- _M_dfs(__match_mode, __state._M_next);
- if (!_M_has_sol)
- _M_rep_once_more(__match_mode, __i);
- }
- else
- {
- // DON'T attempt anything, because there's already another
- // state with higher priority accepted. This state cannot
- // be better by attempting its next node.
- if (!_M_has_sol)
- {
- _M_dfs(__match_mode, __state._M_next);
- // DON'T attempt anything if it's already accepted. An
- // accepted state *must* be better than a solution that
- // matches a non-greedy quantifier one more time.
- if (!_M_has_sol)
- _M_rep_once_more(__match_mode, __i);
- }
- }
- }
- }
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_handle_subexpr_begin(_Match_mode __match_mode, _StateIdT __i)
- {
- const auto& __state = _M_nfa[__i];
- auto& __res = _M_cur_results[__state._M_subexpr];
- auto __back = __res.first;
- __res.first = _M_current;
- _M_dfs(__match_mode, __state._M_next);
- __res.first = __back;
- }
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_handle_subexpr_end(_Match_mode __match_mode, _StateIdT __i)
- {
- const auto& __state = _M_nfa[__i];
- auto& __res = _M_cur_results[__state._M_subexpr];
- auto __back = __res;
- __res.second = _M_current;
- __res.matched = true;
- _M_dfs(__match_mode, __state._M_next);
- __res = __back;
- }
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_handle_line_begin_assertion(_Match_mode __match_mode, _StateIdT __i)
- {
- const auto& __state = _M_nfa[__i];
- if (_M_at_begin())
- _M_dfs(__match_mode, __state._M_next);
- }
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_handle_line_end_assertion(_Match_mode __match_mode, _StateIdT __i)
- {
- const auto& __state = _M_nfa[__i];
- if (_M_at_end())
- _M_dfs(__match_mode, __state._M_next);
- }
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_handle_word_boundary(_Match_mode __match_mode, _StateIdT __i)
- {
- const auto& __state = _M_nfa[__i];
- if (_M_word_boundary() == !__state._M_neg)
- _M_dfs(__match_mode, __state._M_next);
- }
- // Here __state._M_alt offers a single start node for a sub-NFA.
- // We recursively invoke our algorithm to match the sub-NFA.
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_handle_subexpr_lookahead(_Match_mode __match_mode, _StateIdT __i)
- {
- const auto& __state = _M_nfa[__i];
- if (_M_lookahead(__state._M_alt) == !__state._M_neg)
- _M_dfs(__match_mode, __state._M_next);
- }
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_handle_match(_Match_mode __match_mode, _StateIdT __i)
- {
- const auto& __state = _M_nfa[__i];
- if (_M_current == _M_end)
- return;
- if (__dfs_mode)
- {
- if (__state._M_matches(*_M_current))
- {
- ++_M_current;
- _M_dfs(__match_mode, __state._M_next);
- --_M_current;
- }
- }
- else
- if (__state._M_matches(*_M_current))
- _M_states._M_queue(__state._M_next, _M_cur_results);
- }
- template<typename _BiIter, typename _TraitsT>
- struct _Backref_matcher
- {
- _Backref_matcher(bool __icase, const _TraitsT& __traits)
- : _M_traits(__traits) { }
- bool
- _M_apply(_BiIter __expected_begin,
- _BiIter __expected_end, _BiIter __actual_begin,
- _BiIter __actual_end)
- {
- return _M_traits.transform(__expected_begin, __expected_end)
- == _M_traits.transform(__actual_begin, __actual_end);
- }
- const _TraitsT& _M_traits;
- };
- template<typename _BiIter, typename _CharT>
- struct _Backref_matcher<_BiIter, std::regex_traits<_CharT>>
- {
- using _TraitsT = std::regex_traits<_CharT>;
- _Backref_matcher(bool __icase, const _TraitsT& __traits)
- : _M_icase(__icase), _M_traits(__traits) { }
- bool
- _M_apply(_BiIter __expected_begin,
- _BiIter __expected_end, _BiIter __actual_begin,
- _BiIter __actual_end)
- {
- if (!_M_icase)
- return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end,
- __actual_begin, __actual_end);
- typedef std::ctype<_CharT> __ctype_type;
- const auto& __fctyp = use_facet<__ctype_type>(_M_traits.getloc());
- return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end,
- __actual_begin, __actual_end,
- [this, &__fctyp](_CharT __lhs, _CharT __rhs)
- {
- return __fctyp.tolower(__lhs)
- == __fctyp.tolower(__rhs);
- });
- }
- bool _M_icase;
- const _TraitsT& _M_traits;
- };
- // First fetch the matched result from _M_cur_results as __submatch;
- // then compare it with
- // (_M_current, _M_current + (__submatch.second - __submatch.first)).
- // If matched, keep going; else just return and try another state.
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_handle_backref(_Match_mode __match_mode, _StateIdT __i)
- {
- __glibcxx_assert(__dfs_mode);
- const auto& __state = _M_nfa[__i];
- auto& __submatch = _M_cur_results[__state._M_backref_index];
- if (!__submatch.matched)
- return;
- auto __last = _M_current;
- for (auto __tmp = __submatch.first;
- __last != _M_end && __tmp != __submatch.second;
- ++__tmp)
- ++__last;
- if (_Backref_matcher<_BiIter, _TraitsT>(
- _M_re.flags() & regex_constants::icase,
- _M_re._M_automaton->_M_traits)._M_apply(
- __submatch.first, __submatch.second, _M_current, __last))
- {
- if (__last != _M_current)
- {
- auto __backup = _M_current;
- _M_current = __last;
- _M_dfs(__match_mode, __state._M_next);
- _M_current = __backup;
- }
- else
- _M_dfs(__match_mode, __state._M_next);
- }
- }
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_handle_accept(_Match_mode __match_mode, _StateIdT)
- {
- if _GLIBCXX17_CONSTEXPR (__dfs_mode)
- {
- __glibcxx_assert(!_M_has_sol);
- if (__match_mode == _Match_mode::_Exact)
- _M_has_sol = _M_current == _M_end;
- else
- _M_has_sol = true;
- if (_M_current == _M_begin
- && (_M_flags & regex_constants::match_not_null))
- _M_has_sol = false;
- if (_M_has_sol)
- {
- if (_M_nfa._M_flags & regex_constants::ECMAScript)
- _M_results = _M_cur_results;
- else // POSIX
- {
- __glibcxx_assert(_M_states._M_get_sol_pos());
- // Here's POSIX's logic: match the longest one. However
- // we never know which one (lhs or rhs of "|") is longer
- // unless we try both of them and compare the results.
- // The member variable _M_sol_pos records the end
- // position of the last successful match. It's better
- // to be larger, because POSIX regex is always greedy.
- // TODO: This could be slow.
- if (*_M_states._M_get_sol_pos() == _BiIter()
- || std::distance(_M_begin,
- *_M_states._M_get_sol_pos())
- < std::distance(_M_begin, _M_current))
- {
- *_M_states._M_get_sol_pos() = _M_current;
- _M_results = _M_cur_results;
- }
- }
- }
- }
- else
- {
- if (_M_current == _M_begin
- && (_M_flags & regex_constants::match_not_null))
- return;
- if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end)
- if (!_M_has_sol)
- {
- _M_has_sol = true;
- _M_results = _M_cur_results;
- }
- }
- }
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_handle_alternative(_Match_mode __match_mode, _StateIdT __i)
- {
- const auto& __state = _M_nfa[__i];
- if (_M_nfa._M_flags & regex_constants::ECMAScript)
- {
- // TODO: Fix BFS support. It is wrong.
- _M_dfs(__match_mode, __state._M_alt);
- // Pick lhs if it matches. Only try rhs if it doesn't.
- if (!_M_has_sol)
- _M_dfs(__match_mode, __state._M_next);
- }
- else
- {
- // Try both and compare the result.
- // See "case _S_opcode_accept:" handling above.
- _M_dfs(__match_mode, __state._M_alt);
- auto __has_sol = _M_has_sol;
- _M_has_sol = false;
- _M_dfs(__match_mode, __state._M_next);
- _M_has_sol |= __has_sol;
- }
- }
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_dfs(_Match_mode __match_mode, _StateIdT __i)
- {
- if (_M_states._M_visited(__i))
- return;
- switch (_M_nfa[__i]._M_opcode())
- {
- case _S_opcode_repeat:
- _M_handle_repeat(__match_mode, __i); break;
- case _S_opcode_subexpr_begin:
- _M_handle_subexpr_begin(__match_mode, __i); break;
- case _S_opcode_subexpr_end:
- _M_handle_subexpr_end(__match_mode, __i); break;
- case _S_opcode_line_begin_assertion:
- _M_handle_line_begin_assertion(__match_mode, __i); break;
- case _S_opcode_line_end_assertion:
- _M_handle_line_end_assertion(__match_mode, __i); break;
- case _S_opcode_word_boundary:
- _M_handle_word_boundary(__match_mode, __i); break;
- case _S_opcode_subexpr_lookahead:
- _M_handle_subexpr_lookahead(__match_mode, __i); break;
- case _S_opcode_match:
- _M_handle_match(__match_mode, __i); break;
- case _S_opcode_backref:
- _M_handle_backref(__match_mode, __i); break;
- case _S_opcode_accept:
- _M_handle_accept(__match_mode, __i); break;
- case _S_opcode_alternative:
- _M_handle_alternative(__match_mode, __i); break;
- default:
- __glibcxx_assert(false);
- }
- }
- // Return whether now is at some word boundary.
- template<typename _BiIter, typename _Alloc, typename _TraitsT,
- bool __dfs_mode>
- bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
- _M_word_boundary() const
- {
- if (_M_current == _M_begin && (_M_flags & regex_constants::match_not_bow))
- return false;
- if (_M_current == _M_end && (_M_flags & regex_constants::match_not_eow))
- return false;
- bool __left_is_word = false;
- if (_M_current != _M_begin
- || (_M_flags & regex_constants::match_prev_avail))
- {
- auto __prev = _M_current;
- if (_M_is_word(*std::prev(__prev)))
- __left_is_word = true;
- }
- bool __right_is_word =
- _M_current != _M_end && _M_is_word(*_M_current);
- return __left_is_word != __right_is_word;
- }
- } // namespace __detail
- _GLIBCXX_END_NAMESPACE_VERSION
- } // namespace
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