regex_executor.tcc
Go to the documentation of this file.
// class template regex -*- C++ -*-
// Copyright (C) 2013-2014 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)
{
namespace __detail
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _BiIter, typename _Alloc, typename _TraitsT,
bool __dfs_mode>
bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
_M_search()
{
if (_M_flags & regex_constants::match_continuous)
return _M_search_from_first();
auto __cur = _M_begin;
do
{
_M_current = __cur;
if (_M_main<false>())
return true;
}
// Continue when __cur == _M_end
while (__cur++ != _M_end);
return false;
}
// This function operates in different modes, DFS mode or BFS mode, indicated
// by template parameter __dfs_mode. See _M_main for details.
//
// ------------------------------------------------------------
//
// 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: o(match_length), O(2^(_M_nfa.size()))
// Space complexity: \theta(match_results.size() + match_length)
//
// ------------------------------------------------------------
//
// BFS mode:
//
// Russ Cox's article (http://swtch.com/~rsc/regexp/regexp1.html)
// explained this algorithm clearly.
//
// It first computes epsilon closure for every state that's still matching,
// using the same DFS algorithm, but doesn't reenter states (set true in
// _M_visited), nor follows _S_opcode_match.
//
// Then apply DFS using every _S_opcode_match (in _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: o(match_length * match_results.size())
// O(match_length * _M_nfa.size() * match_results.size())
// Space complexity: o(_M_nfa.size() + match_results.size())
// O(_M_nfa.size() * match_results.size())
template<typename _BiIter, typename _Alloc, typename _TraitsT,
bool __dfs_mode>
template<bool __match_mode>
bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
_M_main()
{
if (__dfs_mode)
{
_M_has_sol = false;
_M_cur_results = _M_results;
_M_dfs<__match_mode>(_M_start_state);
return _M_has_sol;
}
else
{
_M_match_queue->push_back(make_pair(_M_start_state, _M_results));
bool __ret = false;
while (1)
{
_M_has_sol = false;
if (_M_match_queue->empty())
break;
_M_visited->assign(_M_visited->size(), false);
auto _M_old_queue = std::move(*_M_match_queue);
for (auto __task : _M_old_queue)
{
_M_cur_results = __task.second;
_M_dfs<__match_mode>(__task.first);
}
if (!__match_mode)
__ret |= _M_has_sol;
if (_M_current == _M_end)
break;
++_M_current;
}
if (__match_mode)
__ret = _M_has_sol;
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(_State<_TraitsT> __state)
{
_ResultsVec __what(_M_cur_results.size());
auto __sub = std::unique_ptr<_Executor>(new _Executor(_M_current,
_M_end,
__what,
_M_re,
_M_flags));
__sub->_M_start_state = __state._M_alt;
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;
}
// TODO: Use a function vector to dispatch, instead of using switch-case.
template<typename _BiIter, typename _Alloc, typename _TraitsT,
bool __dfs_mode>
template<bool __match_mode>
void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
_M_dfs(_StateIdT __i)
{
if (!__dfs_mode)
{
if ((*_M_visited)[__i])
return;
(*_M_visited)[__i] = true;
}
const auto& __state = _M_nfa[__i];
// Every change on _M_cur_results and _M_current will be rolled back after
// finishing the recursion step.
switch (__state._M_opcode)
{
// _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.
case _S_opcode_alternative:
// Greedy.
if (!__state._M_neg)
{
// "Once more" is preferred in greedy mode.
_M_dfs<__match_mode>(__state._M_alt);
// 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_dfs<__match_mode>(__state._M_alt);
}
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_dfs<__match_mode>(__state._M_alt);
}
}
}
break;
case _S_opcode_subexpr_begin:
// If there's nothing changed since last visit, do NOT continue.
// This prevents the executor from get into infinite loop when using
// "()*" to match "".
if (!_M_cur_results[__state._M_subexpr].matched
|| _M_cur_results[__state._M_subexpr].first != _M_current)
{
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;
}
break;
case _S_opcode_subexpr_end:
if (_M_cur_results[__state._M_subexpr].second != _M_current
|| _M_cur_results[__state._M_subexpr].matched != true)
{
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;
}
else
_M_dfs<__match_mode>(__state._M_next);
break;
case _S_opcode_line_begin_assertion:
if (_M_at_begin())
_M_dfs<__match_mode>(__state._M_next);
break;
case _S_opcode_line_end_assertion:
if (_M_at_end())
_M_dfs<__match_mode>(__state._M_next);
break;
case _S_opcode_word_boundary:
if (_M_word_boundary(__state) == !__state._M_neg)
_M_dfs<__match_mode>(__state._M_next);
break;
// Here __state._M_alt offers a single start node for a sub-NFA.
// We recursively invoke our algorithm to match the sub-NFA.
case _S_opcode_subexpr_lookahead:
if (_M_lookahead(__state) == !__state._M_neg)
_M_dfs<__match_mode>(__state._M_next);
break;
case _S_opcode_match:
if (__dfs_mode)
{
if (_M_current != _M_end && __state._M_matches(*_M_current))
{
++_M_current;
_M_dfs<__match_mode>(__state._M_next);
--_M_current;
}
}
else
if (__state._M_matches(*_M_current))
_M_match_queue->push_back(make_pair(__state._M_next,
_M_cur_results));
break;
// 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.
case _S_opcode_backref:
{
_GLIBCXX_DEBUG_ASSERT(__dfs_mode);
auto& __submatch = _M_cur_results[__state._M_backref_index];
if (!__submatch.matched)
break;
auto __last = _M_current;
for (auto __tmp = __submatch.first;
__last != _M_end && __tmp != __submatch.second;
++__tmp)
++__last;
if (_M_re._M_traits.transform(__submatch.first,
__submatch.second)
== _M_re._M_traits.transform(_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);
}
}
break;
case _S_opcode_accept:
if (__dfs_mode)
{
_GLIBCXX_DEBUG_ASSERT(!_M_has_sol);
if (__match_mode)
_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)
_M_results = _M_cur_results;
}
else
{
if (_M_current == _M_begin
&& (_M_flags & regex_constants::match_not_null))
break;
if (!__match_mode || _M_current == _M_end)
if (!_M_has_sol)
{
_M_has_sol = true;
_M_results = _M_cur_results;
}
}
break;
default:
_GLIBCXX_DEBUG_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(_State<_TraitsT> __state) const
{
// By definition.
bool __ans = false;
auto __pre = _M_current;
--__pre;
if (!(_M_at_begin() && _M_at_end()))
{
if (_M_at_begin())
__ans = _M_is_word(*_M_current)
&& !(_M_flags & regex_constants::match_not_bow);
else if (_M_at_end())
__ans = _M_is_word(*__pre)
&& !(_M_flags & regex_constants::match_not_eow);
else
__ans = _M_is_word(*_M_current)
!= _M_is_word(*__pre);
}
return __ans;
}
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace __detail
} // namespace
std::unique_ptr
20.7.1.2 unique_ptr for single objects.
Definition: unique_ptr.h:129
std::regex_constants::match_not_bow
Definition: regex_constants.h:261
std::regex_constants::match_not_eow
Definition: regex_constants.h:267
std::regex_constants::match_not_null
Definition: regex_constants.h:278
std::make_pair
constexpr pair< typename __decay_and_strip< _T1 >::__type, typename __decay_and_strip< _T2 >::__type > make_pair(_T1 &&__x, _T2 &&__y)
A convenience wrapper for creating a pair from two objects.
Definition: stl_pair.h:276
std::regex_constants::match_continuous
Definition: regex_constants.h:283