// class template regex -*- C++ -*-
// Copyright (C) 2013-2015 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_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.get(), _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(_State<_TraitsT> __state)
{
// 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 = __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;
}
// __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--;
}
}
};
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;
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_repeat:
{
// 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);
}
}
}
}
break;
case _S_opcode_subexpr_begin:
{
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:
{
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;
}
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._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 (_M_current == _M_end)
break;
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);
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_automaton->_M_traits.transform(__submatch.first,
__submatch.second)
== _M_re._M_automaton->_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 == _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_DEBUG_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))
break;
if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end)
if (!_M_has_sol)
{
_M_has_sol = true;
_M_results = _M_cur_results;
}
}
break;
case _S_opcode_alternative:
if (_M_nfa._M_flags & regex_constants::ECMAScript)
{
// TODO: Let BFS support ECMAScript's alternative operation.
_GLIBCXX_DEBUG_ASSERT(__dfs_mode);
_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;
}
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() const
{
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);
if (__left_is_word == __right_is_word)
return false;
if (__left_is_word && !(_M_flags & regex_constants::match_not_eow))
return true;
if (__right_is_word && !(_M_flags & regex_constants::match_not_bow))
return true;
return false;
}
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace __detail
} // namespace