1// class template regex -*- C++ -*-
2
3// Copyright (C) 2013-2024 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{
33_GLIBCXX_BEGIN_NAMESPACE_VERSION
34
35namespace __detail
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, start: _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, _M_nfa.size(), false);
126 auto __old_queue = std::move(_M_states._M_match_queue);
127 auto __alloc = _M_cur_results.get_allocator();
128 for (auto& __task : __old_queue)
129 {
130 _M_cur_results = _ResultsVec(std::move(__task.second), __alloc);
131 _M_dfs(__match_mode, start: __task.first);
132 }
133 if (__match_mode == _Match_mode::_Prefix)
134 __ret |= _M_has_sol;
135 if (_M_current == _M_end)
136 break;
137 ++_M_current;
138 }
139 if (__match_mode == _Match_mode::_Exact)
140 __ret = _M_has_sol;
141 _M_states._M_match_queue.clear();
142 return __ret;
143 }
144
145 // Return whether now match the given sub-NFA.
146 template<typename _BiIter, typename _Alloc, typename _TraitsT,
147 bool __dfs_mode>
148 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
149 _M_lookahead(_StateIdT __next)
150 {
151 // Backreferences may refer to captured content.
152 // We may want to make this faster by not copying,
153 // but let's not be clever prematurely.
154 _ResultsVec __what(_M_cur_results);
155 _Executor __sub(_M_current, _M_end, __what, _M_re, _M_flags);
156 __sub._M_states._M_start = __next;
157 if (__sub._M_search_from_first())
158 {
159 for (size_t __i = 0; __i < __what.size(); __i++)
160 if (__what[__i].matched)
161 _M_cur_results[__i] = __what[__i];
162 return true;
163 }
164 return false;
165 }
166
167 // __rep_count records how many times (__rep_count.second)
168 // this node is visited under certain input iterator
169 // (__rep_count.first). This prevent the executor from entering
170 // infinite loop by refusing to continue when it's already been
171 // visited more than twice. It's `twice` instead of `once` because
172 // we need to spare one more time for potential group capture.
173 template<typename _BiIter, typename _Alloc, typename _TraitsT,
174 bool __dfs_mode>
175 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
176 _M_rep_once_more(_Match_mode __match_mode, _StateIdT __i)
177 {
178 const auto& __state = _M_nfa[__i];
179 auto& __rep_count = _M_rep_count[__i];
180 if (__rep_count.second == 0 || __rep_count.first != _M_current)
181 {
182 auto __back = __rep_count;
183 __rep_count.first = _M_current;
184 __rep_count.second = 1;
185 _M_dfs(__match_mode, start: __state._M_alt);
186 __rep_count = __back;
187 }
188 else
189 {
190 if (__rep_count.second < 2)
191 {
192 __rep_count.second++;
193 _M_dfs(__match_mode, start: __state._M_alt);
194 __rep_count.second--;
195 }
196 }
197 }
198
199 // _M_alt branch is "match once more", while _M_next is "get me out
200 // of this quantifier". Executing _M_next first or _M_alt first don't
201 // mean the same thing, and we need to choose the correct order under
202 // given greedy mode.
203 template<typename _BiIter, typename _Alloc, typename _TraitsT,
204 bool __dfs_mode>
205 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
206 _M_handle_repeat(_Match_mode __match_mode, _StateIdT __i)
207 {
208 const auto& __state = _M_nfa[__i];
209
210 // Greedy.
211 if (!__state._M_neg)
212 {
213 _M_rep_once_more(__match_mode, __i);
214 // If it's DFS executor and already accepted, we're done.
215 if (!__dfs_mode || !_M_has_sol)
216 _M_dfs(__match_mode, start: __state._M_next);
217 }
218 else // Non-greedy mode
219 {
220 if (__dfs_mode)
221 {
222 // vice-versa.
223 _M_dfs(__match_mode, start: __state._M_next);
224 if (!_M_has_sol)
225 _M_rep_once_more(__match_mode, __i);
226 }
227 else
228 {
229 // DON'T attempt anything, because there's already another
230 // state with higher priority accepted. This state cannot
231 // be better by attempting its next node.
232 if (!_M_has_sol)
233 {
234 _M_dfs(__match_mode, start: __state._M_next);
235 // DON'T attempt anything if it's already accepted. An
236 // accepted state *must* be better than a solution that
237 // matches a non-greedy quantifier one more time.
238 if (!_M_has_sol)
239 _M_rep_once_more(__match_mode, __i);
240 }
241 }
242 }
243 }
244
245 template<typename _BiIter, typename _Alloc, typename _TraitsT,
246 bool __dfs_mode>
247 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
248 _M_handle_subexpr_begin(_Match_mode __match_mode, _StateIdT __i)
249 {
250 const auto& __state = _M_nfa[__i];
251
252 auto& __res = _M_cur_results[__state._M_subexpr];
253 auto __back = __res.first;
254 __res.first = _M_current;
255 _M_dfs(__match_mode, start: __state._M_next);
256 __res.first = __back;
257 }
258
259 template<typename _BiIter, typename _Alloc, typename _TraitsT,
260 bool __dfs_mode>
261 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
262 _M_handle_subexpr_end(_Match_mode __match_mode, _StateIdT __i)
263 {
264 const auto& __state = _M_nfa[__i];
265
266 auto& __res = _M_cur_results[__state._M_subexpr];
267 auto __back = __res;
268 __res.second = _M_current;
269 __res.matched = true;
270 _M_dfs(__match_mode, start: __state._M_next);
271 __res = __back;
272 }
273
274 template<typename _BiIter, typename _Alloc, typename _TraitsT,
275 bool __dfs_mode>
276 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
277 _M_handle_line_begin_assertion(_Match_mode __match_mode, _StateIdT __i)
278 {
279 const auto& __state = _M_nfa[__i];
280 if (_M_at_begin())
281 _M_dfs(__match_mode, start: __state._M_next);
282 }
283
284 template<typename _BiIter, typename _Alloc, typename _TraitsT,
285 bool __dfs_mode>
286 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
287 _M_handle_line_end_assertion(_Match_mode __match_mode, _StateIdT __i)
288 {
289 const auto& __state = _M_nfa[__i];
290 if (_M_at_end())
291 _M_dfs(__match_mode, start: __state._M_next);
292 }
293
294 template<typename _BiIter, typename _Alloc, typename _TraitsT,
295 bool __dfs_mode>
296 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
297 _M_handle_word_boundary(_Match_mode __match_mode, _StateIdT __i)
298 {
299 const auto& __state = _M_nfa[__i];
300 if (_M_word_boundary() == !__state._M_neg)
301 _M_dfs(__match_mode, start: __state._M_next);
302 }
303
304 // Here __state._M_alt offers a single start node for a sub-NFA.
305 // We recursively invoke our algorithm to match the sub-NFA.
306 template<typename _BiIter, typename _Alloc, typename _TraitsT,
307 bool __dfs_mode>
308 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
309 _M_handle_subexpr_lookahead(_Match_mode __match_mode, _StateIdT __i)
310 {
311 const auto& __state = _M_nfa[__i];
312 if (_M_lookahead(next: __state._M_alt) == !__state._M_neg)
313 _M_dfs(__match_mode, start: __state._M_next);
314 }
315
316 template<typename _BiIter, typename _Alloc, typename _TraitsT,
317 bool __dfs_mode>
318 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
319 _M_handle_match(_Match_mode __match_mode, _StateIdT __i)
320 {
321 const auto& __state = _M_nfa[__i];
322
323 if (_M_current == _M_end)
324 return;
325 if (__dfs_mode)
326 {
327 if (__state._M_matches(*_M_current))
328 {
329 ++_M_current;
330 _M_dfs(__match_mode, start: __state._M_next);
331 --_M_current;
332 }
333 }
334 else
335 if (__state._M_matches(*_M_current))
336 _M_states._M_queue(__state._M_next, _M_cur_results);
337 }
338
339 template<typename _BiIter, typename _TraitsT>
340 struct _Backref_matcher
341 {
342 _Backref_matcher(bool /* __icase */, const _TraitsT& __traits)
343 : _M_traits(__traits) { }
344
345 bool
346 _M_apply(_BiIter __expected_begin,
347 _BiIter __expected_end, _BiIter __actual_begin,
348 _BiIter __actual_end)
349 {
350 return _M_traits.transform(__expected_begin, __expected_end)
351 == _M_traits.transform(__actual_begin, __actual_end);
352 }
353
354 const _TraitsT& _M_traits;
355 };
356
357 template<typename _BiIter, typename _CharT>
358 struct _Backref_matcher<_BiIter, std::regex_traits<_CharT>>
359 {
360 using _TraitsT = std::regex_traits<_CharT>;
361 _Backref_matcher(bool __icase, const _TraitsT& __traits)
362 : _M_icase(__icase), _M_traits(__traits) { }
363
364 bool
365 _M_apply(_BiIter __expected_begin,
366 _BiIter __expected_end, _BiIter __actual_begin,
367 _BiIter __actual_end)
368 {
369 if (!_M_icase)
370 return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end,
371 __actual_begin, __actual_end);
372 typedef std::ctype<_CharT> __ctype_type;
373 const auto& __fctyp = use_facet<__ctype_type>(_M_traits.getloc());
374 return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end,
375 __actual_begin, __actual_end,
376 [this, &__fctyp](_CharT __lhs, _CharT __rhs)
377 {
378 return __fctyp.tolower(__lhs)
379 == __fctyp.tolower(__rhs);
380 });
381 }
382
383 bool _M_icase;
384 const _TraitsT& _M_traits;
385 };
386
387 // First fetch the matched result from _M_cur_results as __submatch;
388 // then compare it with
389 // (_M_current, _M_current + (__submatch.second - __submatch.first)).
390 // If matched, keep going; else just return and try another state.
391 template<typename _BiIter, typename _Alloc, typename _TraitsT,
392 bool __dfs_mode>
393 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
394 _M_handle_backref(_Match_mode __match_mode, _StateIdT __i)
395 {
396 __glibcxx_assert(__dfs_mode);
397
398 const auto& __state = _M_nfa[__i];
399 auto& __submatch = _M_cur_results[__state._M_backref_index];
400 if (!__submatch.matched)
401 return;
402 auto __last = _M_current;
403 for (auto __tmp = __submatch.first;
404 __last != _M_end && __tmp != __submatch.second;
405 ++__tmp)
406 ++__last;
407 if (_Backref_matcher<_BiIter, _TraitsT>(
408 _M_re.flags() & regex_constants::icase,
409 _M_re._M_automaton->_M_traits)._M_apply(
410 __submatch.first, __submatch.second, _M_current, __last))
411 {
412 if (__last != _M_current)
413 {
414 auto __backup = _M_current;
415 _M_current = __last;
416 _M_dfs(__match_mode, start: __state._M_next);
417 _M_current = __backup;
418 }
419 else
420 _M_dfs(__match_mode, start: __state._M_next);
421 }
422 }
423
424 template<typename _BiIter, typename _Alloc, typename _TraitsT,
425 bool __dfs_mode>
426 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
427 _M_handle_accept(_Match_mode __match_mode, _StateIdT)
428 {
429 if _GLIBCXX17_CONSTEXPR (__dfs_mode)
430 {
431 __glibcxx_assert(!_M_has_sol);
432 if (__match_mode == _Match_mode::_Exact)
433 _M_has_sol = _M_current == _M_end;
434 else
435 _M_has_sol = true;
436 if (_M_current == _M_begin
437 && (_M_flags & regex_constants::match_not_null))
438 _M_has_sol = false;
439 if (_M_has_sol)
440 {
441 if (_M_nfa._M_flags & regex_constants::ECMAScript)
442 _M_results = _M_cur_results;
443 else // POSIX
444 {
445 __glibcxx_assert(_M_states._M_get_sol_pos());
446 // Here's POSIX's logic: match the longest one. However
447 // we never know which one (lhs or rhs of "|") is longer
448 // unless we try both of them and compare the results.
449 // The member variable _M_sol_pos records the end
450 // position of the last successful match. It's better
451 // to be larger, because POSIX regex is always greedy.
452 // TODO: This could be slow.
453 if (*_M_states._M_get_sol_pos() == _BiIter()
454 || std::distance(_M_begin,
455 *_M_states._M_get_sol_pos())
456 < std::distance(_M_begin, _M_current))
457 {
458 *_M_states._M_get_sol_pos() = _M_current;
459 _M_results = _M_cur_results;
460 }
461 }
462 }
463 }
464 else
465 {
466 if (_M_current == _M_begin
467 && (_M_flags & regex_constants::match_not_null))
468 return;
469 if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end)
470 if (!_M_has_sol)
471 {
472 _M_has_sol = true;
473 _M_results = _M_cur_results;
474 }
475 }
476 }
477
478 template<typename _BiIter, typename _Alloc, typename _TraitsT,
479 bool __dfs_mode>
480 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
481 _M_handle_alternative(_Match_mode __match_mode, _StateIdT __i)
482 {
483 const auto& __state = _M_nfa[__i];
484
485 if (_M_nfa._M_flags & regex_constants::ECMAScript)
486 {
487 // TODO: Fix BFS support. It is wrong.
488 _M_dfs(__match_mode, start: __state._M_alt);
489 // Pick lhs if it matches. Only try rhs if it doesn't.
490 if (!_M_has_sol)
491 _M_dfs(__match_mode, start: __state._M_next);
492 }
493 else
494 {
495 // Try both and compare the result.
496 // See "case _S_opcode_accept:" handling above.
497 _M_dfs(__match_mode, start: __state._M_alt);
498 auto __has_sol = _M_has_sol;
499 _M_has_sol = false;
500 _M_dfs(__match_mode, start: __state._M_next);
501 _M_has_sol |= __has_sol;
502 }
503 }
504
505 template<typename _BiIter, typename _Alloc, typename _TraitsT,
506 bool __dfs_mode>
507 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
508 _M_dfs(_Match_mode __match_mode, _StateIdT __i)
509 {
510 if (_M_states._M_visited(__i))
511 return;
512
513 switch (_M_nfa[__i]._M_opcode())
514 {
515 case _S_opcode_repeat:
516 _M_handle_repeat(__match_mode, __i); break;
517 case _S_opcode_subexpr_begin:
518 _M_handle_subexpr_begin(__match_mode, __i); break;
519 case _S_opcode_subexpr_end:
520 _M_handle_subexpr_end(__match_mode, __i); break;
521 case _S_opcode_line_begin_assertion:
522 _M_handle_line_begin_assertion(__match_mode, __i); break;
523 case _S_opcode_line_end_assertion:
524 _M_handle_line_end_assertion(__match_mode, __i); break;
525 case _S_opcode_word_boundary:
526 _M_handle_word_boundary(__match_mode, __i); break;
527 case _S_opcode_subexpr_lookahead:
528 _M_handle_subexpr_lookahead(__match_mode, __i); break;
529 case _S_opcode_match:
530 _M_handle_match(__match_mode, __i); break;
531 case _S_opcode_backref:
532 _M_handle_backref(__match_mode, __i); break;
533 case _S_opcode_accept:
534 _M_handle_accept(__match_mode, __i); break;
535 case _S_opcode_alternative:
536 _M_handle_alternative(__match_mode, __i); break;
537 default:
538 __glibcxx_assert(false);
539 }
540 }
541
542 // Return whether now is at some word boundary.
543 template<typename _BiIter, typename _Alloc, typename _TraitsT,
544 bool __dfs_mode>
545 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
546 _M_word_boundary() const
547 {
548 if (_M_current == _M_begin && (_M_flags & regex_constants::match_not_bow))
549 return false;
550 if (_M_current == _M_end && (_M_flags & regex_constants::match_not_eow))
551 return false;
552
553 bool __left_is_word = false;
554 if (_M_current != _M_begin
555 || (_M_flags & regex_constants::match_prev_avail))
556 {
557 auto __prev = _M_current;
558 if (_M_is_word(ch: *std::prev(__prev)))
559 __left_is_word = true;
560 }
561 bool __right_is_word =
562 _M_current != _M_end && _M_is_word(ch: *_M_current);
563
564 return __left_is_word != __right_is_word;
565 }
566} // namespace __detail
567
568_GLIBCXX_END_NAMESPACE_VERSION
569} // namespace
570