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1 // class template regex -*- C++ -*-
3 // Copyright (C) 2013-2014 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
25 /**
26 * @file bits/regex_executor.tcc
27 * This is an internal header file, included by other library headers.
28 * Do not attempt to use it directly. @headername{regex}
29 */
31 namespace std _GLIBCXX_VISIBILITY(default)
32 {
33 namespace __detail
34 {
35 _GLIBCXX_BEGIN_NAMESPACE_VERSION
37 template<typename _BiIter, typename _Alloc, typename _TraitsT,
38 bool __dfs_mode>
39 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
40 _M_search()
41 {
42 if (_M_flags & regex_constants::match_continuous)
43 return _M_search_from_first();
44 auto __cur = _M_begin;
45 do
46 {
47 _M_current = __cur;
48 if (_M_main<false>())
49 return true;
50 }
51 // Continue when __cur == _M_end
52 while (__cur++ != _M_end);
53 return false;
54 }
56 // This function operates in different modes, DFS mode or BFS mode, indicated
57 // by template parameter __dfs_mode. See _M_main for details.
58 //
59 // ------------------------------------------------------------
60 //
61 // DFS mode:
62 //
63 // It applies a Depth-First-Search (aka backtracking) on given NFA and input
64 // string.
65 // At the very beginning the executor stands in the start state, then it tries
66 // every possible state transition in current state recursively. Some state
67 // transitions consume input string, say, a single-char-matcher or a
68 // back-reference matcher; some don't, like assertion or other anchor nodes.
69 // When the input is exhausted and/or the current state is an accepting state,
70 // the whole executor returns true.
71 //
72 // TODO: This approach is exponentially slow for certain input.
73 // Try to compile the NFA to a DFA.
74 //
75 // Time complexity: \Omega(match_length), O(2^(_M_nfa.size()))
76 // Space complexity: \theta(match_results.size() + match_length)
77 //
78 // ------------------------------------------------------------
79 //
80 // BFS mode:
81 //
82 // Russ Cox's article (http://swtch.com/~rsc/regexp/regexp1.html)
83 // explained this algorithm clearly.
84 //
85 // It first computes epsilon closure (states that can be achieved without
86 // consuming characters) for every state that's still matching,
87 // using the same DFS algorithm, but doesn't re-enter states (find a true in
88 // _M_visited), nor follows _S_opcode_match.
89 //
90 // Then apply DFS using every _S_opcode_match (in _M_match_queue) as the start
91 // state.
92 //
93 // It significantly reduces potential duplicate states, so has a better
94 // upper bound; but it requires more overhead.
95 //
96 // Time complexity: \Omega(match_length * match_results.size())
97 // O(match_length * _M_nfa.size() * match_results.size())
98 // Space complexity: \Omega(_M_nfa.size() + match_results.size())
99 // O(_M_nfa.size() * match_results.size())
100 template<typename _BiIter, typename _Alloc, typename _TraitsT,
101 bool __dfs_mode>
102 template<bool __match_mode>
103 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
104 _M_main()
105 {
106 if (__dfs_mode)
107 {
108 _M_has_sol = false;
109 _M_cur_results = _M_results;
110 _M_dfs<__match_mode>(_M_start_state);
111 return _M_has_sol;
112 }
113 else
114 {
115 _M_match_queue->push_back(make_pair(_M_start_state, _M_results));
116 bool __ret = false;
117 while (1)
118 {
119 _M_has_sol = false;
120 if (_M_match_queue->empty())
121 break;
122 _M_visited->assign(_M_visited->size(), false);
123 auto _M_old_queue = std::move(*_M_match_queue);
124 for (auto __task : _M_old_queue)
125 {
126 _M_cur_results = __task.second;
127 _M_dfs<__match_mode>(__task.first);
128 }
129 if (!__match_mode)
130 __ret |= _M_has_sol;
131 if (_M_current == _M_end)
132 break;
133 ++_M_current;
134 }
135 if (__match_mode)
136 __ret = _M_has_sol;
137 return __ret;
138 }
139 }
141 // Return whether now match the given sub-NFA.
142 template<typename _BiIter, typename _Alloc, typename _TraitsT,
143 bool __dfs_mode>
144 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
145 _M_lookahead(_State<_TraitsT> __state)
146 {
147 _ResultsVec __what(_M_cur_results.size());
148 auto __sub = std::unique_ptr<_Executor>(new _Executor(_M_current,
149 _M_end,
150 __what,
151 _M_re,
152 _M_flags));
153 __sub->_M_start_state = __state._M_alt;
154 if (__sub->_M_search_from_first())
155 {
156 for (size_t __i = 0; __i < __what.size(); __i++)
157 if (__what[__i].matched)
158 _M_cur_results[__i] = __what[__i];
159 return true;
160 }
161 return false;
162 }
164 // TODO: Use a function vector to dispatch, instead of using switch-case.
165 template<typename _BiIter, typename _Alloc, typename _TraitsT,
166 bool __dfs_mode>
167 template<bool __match_mode>
168 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
169 _M_dfs(_StateIdT __i)
170 {
171 if (!__dfs_mode)
172 {
173 if ((*_M_visited)[__i])
174 return;
175 (*_M_visited)[__i] = true;
176 }
178 const auto& __state = _M_nfa[__i];
179 // Every change on _M_cur_results and _M_current will be rolled back after
180 // finishing the recursion step.
181 switch (__state._M_opcode)
182 {
183 // _M_alt branch is "match once more", while _M_next is "get me out
184 // of this quantifier". Executing _M_next first or _M_alt first don't
185 // mean the same thing, and we need to choose the correct order under
186 // given greedy mode.
187 case _S_opcode_alternative:
188 // Greedy.
189 if (!__state._M_neg)
190 {
191 // "Once more" is preferred in greedy mode.
192 _M_dfs<__match_mode>(__state._M_alt);
193 // If it's DFS executor and already accepted, we're done.
194 if (!__dfs_mode || !_M_has_sol)
195 _M_dfs<__match_mode>(__state._M_next);
196 }
197 else // Non-greedy mode
198 {
199 if (__dfs_mode)
200 {
201 // vice-versa.
202 _M_dfs<__match_mode>(__state._M_next);
203 if (!_M_has_sol)
204 _M_dfs<__match_mode>(__state._M_alt);
205 }
206 else
207 {
208 // DON'T attempt anything, because there's already another
209 // state with higher priority accepted. This state cannot be
210 // better by attempting its next node.
211 if (!_M_has_sol)
212 {
213 _M_dfs<__match_mode>(__state._M_next);
214 // DON'T attempt anything if it's already accepted. An
215 // accepted state *must* be better than a solution that
216 // matches a non-greedy quantifier one more time.
217 if (!_M_has_sol)
218 _M_dfs<__match_mode>(__state._M_alt);
219 }
220 }
221 }
222 break;
223 case _S_opcode_subexpr_begin:
224 // If there's nothing changed since last visit, do NOT continue.
225 // This prevents the executor from get into infinite loop when using
226 // "()*" to match "".
227 if (!_M_cur_results[__state._M_subexpr].matched
228 || _M_cur_results[__state._M_subexpr].first != _M_current)
229 {
230 auto& __res = _M_cur_results[__state._M_subexpr];
231 auto __back = __res.first;
232 __res.first = _M_current;
233 _M_dfs<__match_mode>(__state._M_next);
234 __res.first = __back;
235 }
236 break;
237 case _S_opcode_subexpr_end:
238 if (_M_cur_results[__state._M_subexpr].second != _M_current
239 || _M_cur_results[__state._M_subexpr].matched != true)
240 {
241 auto& __res = _M_cur_results[__state._M_subexpr];
242 auto __back = __res;
243 __res.second = _M_current;
244 __res.matched = true;
245 _M_dfs<__match_mode>(__state._M_next);
246 __res = __back;
247 }
248 else
249 _M_dfs<__match_mode>(__state._M_next);
250 break;
251 case _S_opcode_line_begin_assertion:
252 if (_M_at_begin())
253 _M_dfs<__match_mode>(__state._M_next);
254 break;
255 case _S_opcode_line_end_assertion:
256 if (_M_at_end())
257 _M_dfs<__match_mode>(__state._M_next);
258 break;
259 case _S_opcode_word_boundary:
260 if (_M_word_boundary(__state) == !__state._M_neg)
261 _M_dfs<__match_mode>(__state._M_next);
262 break;
263 // Here __state._M_alt offers a single start node for a sub-NFA.
264 // We recursively invoke our algorithm to match the sub-NFA.
265 case _S_opcode_subexpr_lookahead:
266 if (_M_lookahead(__state) == !__state._M_neg)
267 _M_dfs<__match_mode>(__state._M_next);
268 break;
269 case _S_opcode_match:
270 if (__dfs_mode)
271 {
272 if (_M_current != _M_end && __state._M_matches(*_M_current))
273 {
274 ++_M_current;
275 _M_dfs<__match_mode>(__state._M_next);
276 --_M_current;
277 }
278 }
279 else
280 if (__state._M_matches(*_M_current))
281 _M_match_queue->push_back(make_pair(__state._M_next,
282 _M_cur_results));
283 break;
284 // First fetch the matched result from _M_cur_results as __submatch;
285 // then compare it with
286 // (_M_current, _M_current + (__submatch.second - __submatch.first)).
287 // If matched, keep going; else just return and try another state.
288 case _S_opcode_backref:
289 {
290 _GLIBCXX_DEBUG_ASSERT(__dfs_mode);
291 auto& __submatch = _M_cur_results[__state._M_backref_index];
292 if (!__submatch.matched)
293 break;
294 auto __last = _M_current;
295 for (auto __tmp = __submatch.first;
296 __last != _M_end && __tmp != __submatch.second;
297 ++__tmp)
298 ++__last;
299 if (_M_re._M_traits.transform(__submatch.first,
300 __submatch.second)
301 == _M_re._M_traits.transform(_M_current, __last))
302 {
303 if (__last != _M_current)
304 {
305 auto __backup = _M_current;
306 _M_current = __last;
307 _M_dfs<__match_mode>(__state._M_next);
308 _M_current = __backup;
309 }
310 else
311 _M_dfs<__match_mode>(__state._M_next);
312 }
313 }
314 break;
315 case _S_opcode_accept:
316 if (__dfs_mode)
317 {
318 _GLIBCXX_DEBUG_ASSERT(!_M_has_sol);
319 if (__match_mode)
320 _M_has_sol = _M_current == _M_end;
321 else
322 _M_has_sol = true;
323 if (_M_current == _M_begin
324 && (_M_flags & regex_constants::match_not_null))
325 _M_has_sol = false;
326 if (_M_has_sol)
327 _M_results = _M_cur_results;
328 }
329 else
330 {
331 if (_M_current == _M_begin
332 && (_M_flags & regex_constants::match_not_null))
333 break;
334 if (!__match_mode || _M_current == _M_end)
335 if (!_M_has_sol)
336 {
337 _M_has_sol = true;
338 _M_results = _M_cur_results;
339 }
340 }
341 break;
342 default:
343 _GLIBCXX_DEBUG_ASSERT(false);
344 }
345 }
347 // Return whether now is at some word boundary.
348 template<typename _BiIter, typename _Alloc, typename _TraitsT,
349 bool __dfs_mode>
350 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
351 _M_word_boundary(_State<_TraitsT> __state) const
352 {
353 // By definition.
354 bool __ans = false;
355 auto __pre = _M_current;
356 --__pre;
357 if (!(_M_at_begin() && _M_at_end()))
358 {
359 if (_M_at_begin())
360 __ans = _M_is_word(*_M_current)
361 && !(_M_flags & regex_constants::match_not_bow);
362 else if (_M_at_end())
363 __ans = _M_is_word(*__pre)
364 && !(_M_flags & regex_constants::match_not_eow);
365 else
366 __ans = _M_is_word(*_M_current)
367 != _M_is_word(*__pre);
368 }
369 return __ans;
370 }
372 _GLIBCXX_END_NAMESPACE_VERSION
373 } // namespace __detail
374 } // namespace