libstdc++
regex_executor.tcc
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1 // class template regex -*- C++ -*-
2 
3 // Copyright (C) 2013-2021 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 
31 namespace std _GLIBCXX_VISIBILITY(default)
32 {
33 _GLIBCXX_BEGIN_NAMESPACE_VERSION
34 
35 namespace __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;
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  template<typename _BiIter, typename _TraitsT>
339  struct _Backref_matcher
340  {
341  _Backref_matcher(bool __icase, const _TraitsT& __traits)
342  : _M_traits(__traits) { }
343 
344  bool
345  _M_apply(_BiIter __expected_begin,
346  _BiIter __expected_end, _BiIter __actual_begin,
347  _BiIter __actual_end)
348  {
349  return _M_traits.transform(__expected_begin, __expected_end)
350  == _M_traits.transform(__actual_begin, __actual_end);
351  }
352 
353  const _TraitsT& _M_traits;
354  };
355 
356  template<typename _BiIter, typename _CharT>
357  struct _Backref_matcher<_BiIter, std::regex_traits<_CharT>>
358  {
359  using _TraitsT = std::regex_traits<_CharT>;
360  _Backref_matcher(bool __icase, const _TraitsT& __traits)
361  : _M_icase(__icase), _M_traits(__traits) { }
362 
363  bool
364  _M_apply(_BiIter __expected_begin,
365  _BiIter __expected_end, _BiIter __actual_begin,
366  _BiIter __actual_end)
367  {
368  if (!_M_icase)
369  return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end,
370  __actual_begin, __actual_end);
371  typedef std::ctype<_CharT> __ctype_type;
372  const auto& __fctyp = use_facet<__ctype_type>(_M_traits.getloc());
373  return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end,
374  __actual_begin, __actual_end,
375  [this, &__fctyp](_CharT __lhs, _CharT __rhs)
376  {
377  return __fctyp.tolower(__lhs)
378  == __fctyp.tolower(__rhs);
379  });
380  }
381 
382  bool _M_icase;
383  const _TraitsT& _M_traits;
384  };
385 
386  // First fetch the matched result from _M_cur_results as __submatch;
387  // then compare it with
388  // (_M_current, _M_current + (__submatch.second - __submatch.first)).
389  // If matched, keep going; else just return and try another state.
390  template<typename _BiIter, typename _Alloc, typename _TraitsT,
391  bool __dfs_mode>
392  void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
393  _M_handle_backref(_Match_mode __match_mode, _StateIdT __i)
394  {
395  __glibcxx_assert(__dfs_mode);
396 
397  const auto& __state = _M_nfa[__i];
398  auto& __submatch = _M_cur_results[__state._M_backref_index];
399  if (!__submatch.matched)
400  return;
401  auto __last = _M_current;
402  for (auto __tmp = __submatch.first;
403  __last != _M_end && __tmp != __submatch.second;
404  ++__tmp)
405  ++__last;
406  if (_Backref_matcher<_BiIter, _TraitsT>(
407  _M_re.flags() & regex_constants::icase,
408  _M_re._M_automaton->_M_traits)._M_apply(
409  __submatch.first, __submatch.second, _M_current, __last))
410  {
411  if (__last != _M_current)
412  {
413  auto __backup = _M_current;
414  _M_current = __last;
415  _M_dfs(__match_mode, __state._M_next);
416  _M_current = __backup;
417  }
418  else
419  _M_dfs(__match_mode, __state._M_next);
420  }
421  }
422 
423  template<typename _BiIter, typename _Alloc, typename _TraitsT,
424  bool __dfs_mode>
425  void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
426  _M_handle_accept(_Match_mode __match_mode, _StateIdT __i)
427  {
428  if (__dfs_mode)
429  {
430  __glibcxx_assert(!_M_has_sol);
431  if (__match_mode == _Match_mode::_Exact)
432  _M_has_sol = _M_current == _M_end;
433  else
434  _M_has_sol = true;
435  if (_M_current == _M_begin
436  && (_M_flags & regex_constants::match_not_null))
437  _M_has_sol = false;
438  if (_M_has_sol)
439  {
440  if (_M_nfa._M_flags & regex_constants::ECMAScript)
441  _M_results = _M_cur_results;
442  else // POSIX
443  {
444  __glibcxx_assert(_M_states._M_get_sol_pos());
445  // Here's POSIX's logic: match the longest one. However
446  // we never know which one (lhs or rhs of "|") is longer
447  // unless we try both of them and compare the results.
448  // The member variable _M_sol_pos records the end
449  // position of the last successful match. It's better
450  // to be larger, because POSIX regex is always greedy.
451  // TODO: This could be slow.
452  if (*_M_states._M_get_sol_pos() == _BiIter()
453  || std::distance(_M_begin,
454  *_M_states._M_get_sol_pos())
455  < std::distance(_M_begin, _M_current))
456  {
457  *_M_states._M_get_sol_pos() = _M_current;
458  _M_results = _M_cur_results;
459  }
460  }
461  }
462  }
463  else
464  {
465  if (_M_current == _M_begin
466  && (_M_flags & regex_constants::match_not_null))
467  return;
468  if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end)
469  if (!_M_has_sol)
470  {
471  _M_has_sol = true;
472  _M_results = _M_cur_results;
473  }
474  }
475  }
476 
477  template<typename _BiIter, typename _Alloc, typename _TraitsT,
478  bool __dfs_mode>
479  void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
480  _M_handle_alternative(_Match_mode __match_mode, _StateIdT __i)
481  {
482  const auto& __state = _M_nfa[__i];
483 
484  if (_M_nfa._M_flags & regex_constants::ECMAScript)
485  {
486  // TODO: Fix BFS support. It is wrong.
487  _M_dfs(__match_mode, __state._M_alt);
488  // Pick lhs if it matches. Only try rhs if it doesn't.
489  if (!_M_has_sol)
490  _M_dfs(__match_mode, __state._M_next);
491  }
492  else
493  {
494  // Try both and compare the result.
495  // See "case _S_opcode_accept:" handling above.
496  _M_dfs(__match_mode, __state._M_alt);
497  auto __has_sol = _M_has_sol;
498  _M_has_sol = false;
499  _M_dfs(__match_mode, __state._M_next);
500  _M_has_sol |= __has_sol;
501  }
502  }
503 
504  template<typename _BiIter, typename _Alloc, typename _TraitsT,
505  bool __dfs_mode>
506  void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
507  _M_dfs(_Match_mode __match_mode, _StateIdT __i)
508  {
509  if (_M_states._M_visited(__i))
510  return;
511 
512  switch (_M_nfa[__i]._M_opcode())
513  {
514  case _S_opcode_repeat:
515  _M_handle_repeat(__match_mode, __i); break;
516  case _S_opcode_subexpr_begin:
517  _M_handle_subexpr_begin(__match_mode, __i); break;
518  case _S_opcode_subexpr_end:
519  _M_handle_subexpr_end(__match_mode, __i); break;
520  case _S_opcode_line_begin_assertion:
521  _M_handle_line_begin_assertion(__match_mode, __i); break;
522  case _S_opcode_line_end_assertion:
523  _M_handle_line_end_assertion(__match_mode, __i); break;
524  case _S_opcode_word_boundary:
525  _M_handle_word_boundary(__match_mode, __i); break;
526  case _S_opcode_subexpr_lookahead:
527  _M_handle_subexpr_lookahead(__match_mode, __i); break;
528  case _S_opcode_match:
529  _M_handle_match(__match_mode, __i); break;
530  case _S_opcode_backref:
531  _M_handle_backref(__match_mode, __i); break;
532  case _S_opcode_accept:
533  _M_handle_accept(__match_mode, __i); break;
534  case _S_opcode_alternative:
535  _M_handle_alternative(__match_mode, __i); break;
536  default:
537  __glibcxx_assert(false);
538  }
539  }
540 
541  // Return whether now is at some word boundary.
542  template<typename _BiIter, typename _Alloc, typename _TraitsT,
543  bool __dfs_mode>
544  bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
545  _M_word_boundary() const
546  {
547  if (_M_current == _M_begin && (_M_flags & regex_constants::match_not_bow))
548  return false;
549  if (_M_current == _M_end && (_M_flags & regex_constants::match_not_eow))
550  return false;
551 
552  bool __left_is_word = false;
553  if (_M_current != _M_begin
554  || (_M_flags & regex_constants::match_prev_avail))
555  {
556  auto __prev = _M_current;
557  if (_M_is_word(*std::prev(__prev)))
558  __left_is_word = true;
559  }
560  bool __right_is_word =
561  _M_current != _M_end && _M_is_word(*_M_current);
562 
563  return __left_is_word != __right_is_word;
564  }
565 } // namespace __detail
566 
567 _GLIBCXX_END_NAMESPACE_VERSION
568 } // namespace
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:104
ISO C++ entities toplevel namespace is std.
constexpr match_flag_type match_not_bow
constexpr syntax_option_type ECMAScript
constexpr match_flag_type match_continuous
constexpr syntax_option_type icase
constexpr match_flag_type match_prev_avail
constexpr match_flag_type match_not_eow
constexpr match_flag_type match_not_null
Primary class template ctype facet.
Describes aspects of a regular expression.
Definition: regex.h:81