1// class template regex -*- C++ -*-
2
3// Copyright (C) 2013-2017 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.
10
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.
15
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.
19
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/>.
24
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 */
30
31namespace std _GLIBCXX_VISIBILITY(default)
32{
33namespace __detail
34{
35_GLIBCXX_BEGIN_NAMESPACE_VERSION
36
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_search_from_first())
43 return true;
44 if (_M_flags & regex_constants::match_continuous)
45 return false;
46 _M_flags |= regex_constants::match_prev_avail;
47 while (_M_begin != _M_end)
48 {
49 ++_M_begin;
50 if (_M_search_from_first())
51 return true;
52 }
53 return false;
54 }
55
56 // The _M_main function operates in different modes, DFS mode or BFS mode,
57 // indicated by template parameter __dfs_mode, and dispatches to one of the
58 // _M_main_dispatch overloads.
59 //
60 // ------------------------------------------------------------
61 //
62 // DFS mode:
63 //
64 // It applies a Depth-First-Search (aka backtracking) on given NFA and input
65 // string.
66 // At the very beginning the executor stands in the start state, then it
67 // tries every possible state transition in current state recursively. Some
68 // state transitions consume input string, say, a single-char-matcher or a
69 // back-reference matcher; some don't, like assertion or other anchor nodes.
70 // When the input is exhausted and/or the current state is an accepting
71 // state, the whole executor returns true.
72 //
73 // TODO: This approach is exponentially slow for certain input.
74 // Try to compile the NFA to a DFA.
75 //
76 // Time complexity: \Omega(match_length), O(2^(_M_nfa.size()))
77 // Space complexity: \theta(match_results.size() + match_length)
78 //
79 template<typename _BiIter, typename _Alloc, typename _TraitsT,
80 bool __dfs_mode>
81 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
82 _M_main_dispatch(_Match_mode __match_mode, __dfs)
83 {
84 _M_has_sol = false;
85 *_M_states._M_get_sol_pos() = _BiIter();
86 _M_cur_results = _M_results;
87 _M_dfs(__match_mode, _M_states._M_start);
88 return _M_has_sol;
89 }
90
91 // ------------------------------------------------------------
92 //
93 // BFS mode:
94 //
95 // Russ Cox's article (http://swtch.com/~rsc/regexp/regexp1.html)
96 // explained this algorithm clearly.
97 //
98 // It first computes epsilon closure (states that can be achieved without
99 // consuming characters) for every state that's still matching,
100 // using the same DFS algorithm, but doesn't re-enter states (using
101 // _M_states._M_visited to check), nor follow _S_opcode_match.
102 //
103 // Then apply DFS using every _S_opcode_match (in _M_states._M_match_queue)
104 // as the start state.
105 //
106 // It significantly reduces potential duplicate states, so has a better
107 // upper bound; but it requires more overhead.
108 //
109 // Time complexity: \Omega(match_length * match_results.size())
110 // O(match_length * _M_nfa.size() * match_results.size())
111 // Space complexity: \Omega(_M_nfa.size() + match_results.size())
112 // O(_M_nfa.size() * match_results.size())
113 template<typename _BiIter, typename _Alloc, typename _TraitsT,
114 bool __dfs_mode>
115 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
116 _M_main_dispatch(_Match_mode __match_mode, __bfs)
117 {
118 _M_states._M_queue(_M_states._M_start, _M_results);
119 bool __ret = false;
120 while (1)
121 {
122 _M_has_sol = false;
123 if (_M_states._M_match_queue.empty())
124 break;
125 std::fill_n(_M_states._M_visited_states.get(), _M_nfa.size(), false);
126 auto __old_queue = std::move(_M_states._M_match_queue);
127 for (auto& __task : __old_queue)
128 {
129 _M_cur_results = std::move(__task.second);
130 _M_dfs(__match_mode, __task.first);
131 }
132 if (__match_mode == _Match_mode::_Prefix)
133 __ret |= _M_has_sol;
134 if (_M_current == _M_end)
135 break;
136 ++_M_current;
137 }
138 if (__match_mode == _Match_mode::_Exact)
139 __ret = _M_has_sol;
140 _M_states._M_match_queue.clear();
141 return __ret;
142 }
143
144 // Return whether now match the given sub-NFA.
145 template<typename _BiIter, typename _Alloc, typename _TraitsT,
146 bool __dfs_mode>
147 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
148 _M_lookahead(_StateIdT __next)
149 {
150 // Backreferences may refer to captured content.
151 // We may want to make this faster by not copying,
152 // but let's not be clever prematurely.
153 _ResultsVec __what(_M_cur_results);
154 _Executor __sub(_M_current, _M_end, __what, _M_re, _M_flags);
155 __sub._M_states._M_start = __next;
156 if (__sub._M_search_from_first())
157 {
158 for (size_t __i = 0; __i < __what.size(); __i++)
159 if (__what[__i].matched)
160 _M_cur_results[__i] = __what[__i];
161 return true;
162 }
163 return false;
164 }
165
166 // __rep_count records how many times (__rep_count.second)
167 // this node is visited under certain input iterator
168 // (__rep_count.first). This prevent the executor from entering
169 // infinite loop by refusing to continue when it's already been
170 // visited more than twice. It's `twice` instead of `once` because
171 // we need to spare one more time for potential group capture.
172 template<typename _BiIter, typename _Alloc, typename _TraitsT,
173 bool __dfs_mode>
174 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
175 _M_rep_once_more(_Match_mode __match_mode, _StateIdT __i)
176 {
177 const auto& __state = _M_nfa[__i];
178 auto& __rep_count = _M_rep_count[__i];
179 if (__rep_count.second == 0 || __rep_count.first != _M_current)
180 {
181 auto __back = __rep_count;
182 __rep_count.first = _M_current;
183 __rep_count.second = 1;
184 _M_dfs(__match_mode, __state._M_alt);
185 __rep_count = __back;
186 }
187 else
188 {
189 if (__rep_count.second < 2)
190 {
191 __rep_count.second++;
192 _M_dfs(__match_mode, __state._M_alt);
193 __rep_count.second--;
194 }
195 }
196 };
197
198 // _M_alt branch is "match once more", while _M_next is "get me out
199 // of this quantifier". Executing _M_next first or _M_alt first don't
200 // mean the same thing, and we need to choose the correct order under
201 // given greedy mode.
202 template<typename _BiIter, typename _Alloc, typename _TraitsT,
203 bool __dfs_mode>
204 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
205 _M_handle_repeat(_Match_mode __match_mode, _StateIdT __i)
206 {
207 const auto& __state = _M_nfa[__i];
208
209 // Greedy.
210 if (!__state._M_neg)
211 {
212 _M_rep_once_more(__match_mode, __i);
213 // If it's DFS executor and already accepted, we're done.
214 if (!__dfs_mode || !_M_has_sol)
215 _M_dfs(__match_mode, __state._M_next);
216 }
217 else // Non-greedy mode
218 {
219 if (__dfs_mode)
220 {
221 // vice-versa.
222 _M_dfs(__match_mode, __state._M_next);
223 if (!_M_has_sol)
224 _M_rep_once_more(__match_mode, __i);
225 }
226 else
227 {
228 // DON'T attempt anything, because there's already another
229 // state with higher priority accepted. This state cannot
230 // be better by attempting its next node.
231 if (!_M_has_sol)
232 {
233 _M_dfs(__match_mode, __state._M_next);
234 // DON'T attempt anything if it's already accepted. An
235 // accepted state *must* be better than a solution that
236 // matches a non-greedy quantifier one more time.
237 if (!_M_has_sol)
238 _M_rep_once_more(__match_mode, __i);
239 }
240 }
241 }
242 }
243
244 template<typename _BiIter, typename _Alloc, typename _TraitsT,
245 bool __dfs_mode>
246 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
247 _M_handle_subexpr_begin(_Match_mode __match_mode, _StateIdT __i)
248 {
249 const auto& __state = _M_nfa[__i];
250
251 auto& __res = _M_cur_results[__state._M_subexpr];
252 auto __back = __res.first;
253 __res.first = _M_current;
254 _M_dfs(__match_mode, __state._M_next);
255 __res.first = __back;
256 }
257
258 template<typename _BiIter, typename _Alloc, typename _TraitsT,
259 bool __dfs_mode>
260 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
261 _M_handle_subexpr_end(_Match_mode __match_mode, _StateIdT __i)
262 {
263 const auto& __state = _M_nfa[__i];
264
265 auto& __res = _M_cur_results[__state._M_subexpr];
266 auto __back = __res;
267 __res.second = _M_current;
268 __res.matched = true;
269 _M_dfs(__match_mode, __state._M_next);
270 __res = __back;
271 }
272
273 template<typename _BiIter, typename _Alloc, typename _TraitsT,
274 bool __dfs_mode>
275 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
276 _M_handle_line_begin_assertion(_Match_mode __match_mode, _StateIdT __i)
277 {
278 const auto& __state = _M_nfa[__i];
279 if (_M_at_begin())
280 _M_dfs(__match_mode, __state._M_next);
281 }
282
283 template<typename _BiIter, typename _Alloc, typename _TraitsT,
284 bool __dfs_mode>
285 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
286 _M_handle_line_end_assertion(_Match_mode __match_mode, _StateIdT __i)
287 {
288 const auto& __state = _M_nfa[__i];
289 if (_M_at_end())
290 _M_dfs(__match_mode, __state._M_next);
291 }
292
293 template<typename _BiIter, typename _Alloc, typename _TraitsT,
294 bool __dfs_mode>
295 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
296 _M_handle_word_boundary(_Match_mode __match_mode, _StateIdT __i)
297 {
298 const auto& __state = _M_nfa[__i];
299 if (_M_word_boundary() == !__state._M_neg)
300 _M_dfs(__match_mode, __state._M_next);
301 }
302
303 // Here __state._M_alt offers a single start node for a sub-NFA.
304 // We recursively invoke our algorithm to match the sub-NFA.
305 template<typename _BiIter, typename _Alloc, typename _TraitsT,
306 bool __dfs_mode>
307 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
308 _M_handle_subexpr_lookahead(_Match_mode __match_mode, _StateIdT __i)
309 {
310 const auto& __state = _M_nfa[__i];
311 if (_M_lookahead(__state._M_alt) == !__state._M_neg)
312 _M_dfs(__match_mode, __state._M_next);
313 }
314
315 template<typename _BiIter, typename _Alloc, typename _TraitsT,
316 bool __dfs_mode>
317 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
318 _M_handle_match(_Match_mode __match_mode, _StateIdT __i)
319 {
320 const auto& __state = _M_nfa[__i];
321
322 if (_M_current == _M_end)
323 return;
324 if (__dfs_mode)
325 {
326 if (__state._M_matches(*_M_current))
327 {
328 ++_M_current;
329 _M_dfs(__match_mode, __state._M_next);
330 --_M_current;
331 }
332 }
333 else
334 if (__state._M_matches(*_M_current))
335 _M_states._M_queue(__state._M_next, _M_cur_results);
336 }
337
338 // First fetch the matched result from _M_cur_results as __submatch;
339 // then compare it with
340 // (_M_current, _M_current + (__submatch.second - __submatch.first)).
341 // If matched, keep going; else just return and try another state.
342 template<typename _BiIter, typename _Alloc, typename _TraitsT,
343 bool __dfs_mode>
344 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
345 _M_handle_backref(_Match_mode __match_mode, _StateIdT __i)
346 {
347 __glibcxx_assert(__dfs_mode);
348
349 const auto& __state = _M_nfa[__i];
350 auto& __submatch = _M_cur_results[__state._M_backref_index];
351 if (!__submatch.matched)
352 return;
353 auto __last = _M_current;
354 for (auto __tmp = __submatch.first;
355 __last != _M_end && __tmp != __submatch.second;
356 ++__tmp)
357 ++__last;
358 if (_M_re._M_automaton->_M_traits.transform(__submatch.first,
359 __submatch.second)
360 == _M_re._M_automaton->_M_traits.transform(_M_current, __last))
361 {
362 if (__last != _M_current)
363 {
364 auto __backup = _M_current;
365 _M_current = __last;
366 _M_dfs(__match_mode, __state._M_next);
367 _M_current = __backup;
368 }
369 else
370 _M_dfs(__match_mode, __state._M_next);
371 }
372 }
373
374 template<typename _BiIter, typename _Alloc, typename _TraitsT,
375 bool __dfs_mode>
376 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
377 _M_handle_accept(_Match_mode __match_mode, _StateIdT __i)
378 {
379 if (__dfs_mode)
380 {
381 __glibcxx_assert(!_M_has_sol);
382 if (__match_mode == _Match_mode::_Exact)
383 _M_has_sol = _M_current == _M_end;
384 else
385 _M_has_sol = true;
386 if (_M_current == _M_begin
387 && (_M_flags & regex_constants::match_not_null))
388 _M_has_sol = false;
389 if (_M_has_sol)
390 {
391 if (_M_nfa._M_flags & regex_constants::ECMAScript)
392 _M_results = _M_cur_results;
393 else // POSIX
394 {
395 __glibcxx_assert(_M_states._M_get_sol_pos());
396 // Here's POSIX's logic: match the longest one. However
397 // we never know which one (lhs or rhs of "|") is longer
398 // unless we try both of them and compare the results.
399 // The member variable _M_sol_pos records the end
400 // position of the last successful match. It's better
401 // to be larger, because POSIX regex is always greedy.
402 // TODO: This could be slow.
403 if (*_M_states._M_get_sol_pos() == _BiIter()
404 || std::distance(_M_begin,
405 *_M_states._M_get_sol_pos())
406 < std::distance(_M_begin, _M_current))
407 {
408 *_M_states._M_get_sol_pos() = _M_current;
409 _M_results = _M_cur_results;
410 }
411 }
412 }
413 }
414 else
415 {
416 if (_M_current == _M_begin
417 && (_M_flags & regex_constants::match_not_null))
418 return;
419 if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end)
420 if (!_M_has_sol)
421 {
422 _M_has_sol = true;
423 _M_results = _M_cur_results;
424 }
425 }
426 }
427
428 template<typename _BiIter, typename _Alloc, typename _TraitsT,
429 bool __dfs_mode>
430 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
431 _M_handle_alternative(_Match_mode __match_mode, _StateIdT __i)
432 {
433 const auto& __state = _M_nfa[__i];
434
435 if (_M_nfa._M_flags & regex_constants::ECMAScript)
436 {
437 // TODO: Fix BFS support. It is wrong.
438 _M_dfs(__match_mode, __state._M_alt);
439 // Pick lhs if it matches. Only try rhs if it doesn't.
440 if (!_M_has_sol)
441 _M_dfs(__match_mode, __state._M_next);
442 }
443 else
444 {
445 // Try both and compare the result.
446 // See "case _S_opcode_accept:" handling above.
447 _M_dfs(__match_mode, __state._M_alt);
448 auto __has_sol = _M_has_sol;
449 _M_has_sol = false;
450 _M_dfs(__match_mode, __state._M_next);
451 _M_has_sol |= __has_sol;
452 }
453 }
454
455 template<typename _BiIter, typename _Alloc, typename _TraitsT,
456 bool __dfs_mode>
457 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
458 _M_dfs(_Match_mode __match_mode, _StateIdT __i)
459 {
460 if (_M_states._M_visited(__i))
461 return;
462
463 switch (_M_nfa[__i]._M_opcode())
464 {
465 case _S_opcode_repeat:
466 _M_handle_repeat(__match_mode, __i); break;
467 case _S_opcode_subexpr_begin:
468 _M_handle_subexpr_begin(__match_mode, __i); break;
469 case _S_opcode_subexpr_end:
470 _M_handle_subexpr_end(__match_mode, __i); break;
471 case _S_opcode_line_begin_assertion:
472 _M_handle_line_begin_assertion(__match_mode, __i); break;
473 case _S_opcode_line_end_assertion:
474 _M_handle_line_end_assertion(__match_mode, __i); break;
475 case _S_opcode_word_boundary:
476 _M_handle_word_boundary(__match_mode, __i); break;
477 case _S_opcode_subexpr_lookahead:
478 _M_handle_subexpr_lookahead(__match_mode, __i); break;
479 case _S_opcode_match:
480 _M_handle_match(__match_mode, __i); break;
481 case _S_opcode_backref:
482 _M_handle_backref(__match_mode, __i); break;
483 case _S_opcode_accept:
484 _M_handle_accept(__match_mode, __i); break;
485 case _S_opcode_alternative:
486 _M_handle_alternative(__match_mode, __i); break;
487 default:
488 __glibcxx_assert(false);
489 }
490 }
491
492 // Return whether now is at some word boundary.
493 template<typename _BiIter, typename _Alloc, typename _TraitsT,
494 bool __dfs_mode>
495 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
496 _M_word_boundary() const
497 {
498 if (_M_current == _M_begin && (_M_flags & regex_constants::match_not_bow))
499 return false;
500 if (_M_current == _M_end && (_M_flags & regex_constants::match_not_eow))
501 return false;
502
503 bool __left_is_word = false;
504 if (_M_current != _M_begin
505 || (_M_flags & regex_constants::match_prev_avail))
506 {
507 auto __prev = _M_current;
508 if (_M_is_word(*std::prev(__prev)))
509 __left_is_word = true;
510 }
511 bool __right_is_word =
512 _M_current != _M_end && _M_is_word(*_M_current);
513
514 return __left_is_word != __right_is_word;
515 }
516
517_GLIBCXX_END_NAMESPACE_VERSION
518} // namespace __detail
519} // namespace
520