libstdc++
regex_executor.tcc
1 // class template regex -*- C++ -*-
2 
3 // Copyright (C) 2013-2015 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 namespace __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(_State<_TraitsT> __state)
149  {
150  _ResultsVec __what(_M_cur_results.size());
151  _Executor __sub(_M_current, _M_end, __what, _M_re, _M_flags);
152  __sub._M_states._M_start = __state._M_alt;
153  if (__sub._M_search_from_first())
154  {
155  for (size_t __i = 0; __i < __what.size(); __i++)
156  if (__what[__i].matched)
157  _M_cur_results[__i] = __what[__i];
158  return true;
159  }
160  return false;
161  }
162 
163  // __rep_count records how many times (__rep_count.second)
164  // this node is visited under certain input iterator
165  // (__rep_count.first). This prevent the executor from entering
166  // infinite loop by refusing to continue when it's already been
167  // visited more than twice. It's `twice` instead of `once` because
168  // we need to spare one more time for potential group capture.
169  template<typename _BiIter, typename _Alloc, typename _TraitsT,
170  bool __dfs_mode>
171  void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
172  _M_rep_once_more(_Match_mode __match_mode, _StateIdT __i)
173  {
174  const auto& __state = _M_nfa[__i];
175  auto& __rep_count = _M_rep_count[__i];
176  if (__rep_count.second == 0 || __rep_count.first != _M_current)
177  {
178  auto __back = __rep_count;
179  __rep_count.first = _M_current;
180  __rep_count.second = 1;
181  _M_dfs(__match_mode, __state._M_alt);
182  __rep_count = __back;
183  }
184  else
185  {
186  if (__rep_count.second < 2)
187  {
188  __rep_count.second++;
189  _M_dfs(__match_mode, __state._M_alt);
190  __rep_count.second--;
191  }
192  }
193  };
194 
195  template<typename _BiIter, typename _Alloc, typename _TraitsT,
196  bool __dfs_mode>
197  void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
198  _M_dfs(_Match_mode __match_mode, _StateIdT __i)
199  {
200  if (_M_states._M_visited(__i))
201  return;
202 
203  const auto& __state = _M_nfa[__i];
204  // Every change on _M_cur_results and _M_current will be rolled back after
205  // finishing the recursion step.
206  switch (__state._M_opcode)
207  {
208  // _M_alt branch is "match once more", while _M_next is "get me out
209  // of this quantifier". Executing _M_next first or _M_alt first don't
210  // mean the same thing, and we need to choose the correct order under
211  // given greedy mode.
212  case _S_opcode_repeat:
213  {
214  // Greedy.
215  if (!__state._M_neg)
216  {
217  _M_rep_once_more(__match_mode, __i);
218  // If it's DFS executor and already accepted, we're done.
219  if (!__dfs_mode || !_M_has_sol)
220  _M_dfs(__match_mode, __state._M_next);
221  }
222  else // Non-greedy mode
223  {
224  if (__dfs_mode)
225  {
226  // vice-versa.
227  _M_dfs(__match_mode, __state._M_next);
228  if (!_M_has_sol)
229  _M_rep_once_more(__match_mode, __i);
230  }
231  else
232  {
233  // DON'T attempt anything, because there's already another
234  // state with higher priority accepted. This state cannot
235  // be better by attempting its next node.
236  if (!_M_has_sol)
237  {
238  _M_dfs(__match_mode, __state._M_next);
239  // DON'T attempt anything if it's already accepted. An
240  // accepted state *must* be better than a solution that
241  // matches a non-greedy quantifier one more time.
242  if (!_M_has_sol)
243  _M_rep_once_more(__match_mode, __i);
244  }
245  }
246  }
247  }
248  break;
249  case _S_opcode_subexpr_begin:
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  break;
258  case _S_opcode_subexpr_end:
259  {
260  auto& __res = _M_cur_results[__state._M_subexpr];
261  auto __back = __res;
262  __res.second = _M_current;
263  __res.matched = true;
264  _M_dfs(__match_mode, __state._M_next);
265  __res = __back;
266  }
267  break;
268  case _S_opcode_line_begin_assertion:
269  if (_M_at_begin())
270  _M_dfs(__match_mode, __state._M_next);
271  break;
272  case _S_opcode_line_end_assertion:
273  if (_M_at_end())
274  _M_dfs(__match_mode, __state._M_next);
275  break;
276  case _S_opcode_word_boundary:
277  if (_M_word_boundary() == !__state._M_neg)
278  _M_dfs(__match_mode, __state._M_next);
279  break;
280  // Here __state._M_alt offers a single start node for a sub-NFA.
281  // We recursively invoke our algorithm to match the sub-NFA.
282  case _S_opcode_subexpr_lookahead:
283  if (_M_lookahead(__state) == !__state._M_neg)
284  _M_dfs(__match_mode, __state._M_next);
285  break;
286  case _S_opcode_match:
287  if (_M_current == _M_end)
288  break;
289  if (__dfs_mode)
290  {
291  if (__state._M_matches(*_M_current))
292  {
293  ++_M_current;
294  _M_dfs(__match_mode, __state._M_next);
295  --_M_current;
296  }
297  }
298  else
299  if (__state._M_matches(*_M_current))
300  _M_states._M_queue(__state._M_next, _M_cur_results);
301  break;
302  // First fetch the matched result from _M_cur_results as __submatch;
303  // then compare it with
304  // (_M_current, _M_current + (__submatch.second - __submatch.first)).
305  // If matched, keep going; else just return and try another state.
306  case _S_opcode_backref:
307  {
308  _GLIBCXX_DEBUG_ASSERT(__dfs_mode);
309  auto& __submatch = _M_cur_results[__state._M_backref_index];
310  if (!__submatch.matched)
311  break;
312  auto __last = _M_current;
313  for (auto __tmp = __submatch.first;
314  __last != _M_end && __tmp != __submatch.second;
315  ++__tmp)
316  ++__last;
317  if (_M_re._M_automaton->_M_traits.transform(__submatch.first,
318  __submatch.second)
319  == _M_re._M_automaton->_M_traits.transform(_M_current, __last))
320  {
321  if (__last != _M_current)
322  {
323  auto __backup = _M_current;
324  _M_current = __last;
325  _M_dfs(__match_mode, __state._M_next);
326  _M_current = __backup;
327  }
328  else
329  _M_dfs(__match_mode, __state._M_next);
330  }
331  }
332  break;
333  case _S_opcode_accept:
334  if (__dfs_mode)
335  {
336  _GLIBCXX_DEBUG_ASSERT(!_M_has_sol);
337  if (__match_mode == _Match_mode::_Exact)
338  _M_has_sol = _M_current == _M_end;
339  else
340  _M_has_sol = true;
341  if (_M_current == _M_begin
342  && (_M_flags & regex_constants::match_not_null))
343  _M_has_sol = false;
344  if (_M_has_sol)
345  {
346  if (_M_nfa._M_flags & regex_constants::ECMAScript)
347  _M_results = _M_cur_results;
348  else // POSIX
349  {
350  _GLIBCXX_DEBUG_ASSERT(_M_states._M_get_sol_pos());
351  // Here's POSIX's logic: match the longest one. However
352  // we never know which one (lhs or rhs of "|") is longer
353  // unless we try both of them and compare the results.
354  // The member variable _M_sol_pos records the end
355  // position of the last successful match. It's better
356  // to be larger, because POSIX regex is always greedy.
357  // TODO: This could be slow.
358  if (*_M_states._M_get_sol_pos() == _BiIter()
359  || std::distance(_M_begin,
360  *_M_states._M_get_sol_pos())
361  < std::distance(_M_begin, _M_current))
362  {
363  *_M_states._M_get_sol_pos() = _M_current;
364  _M_results = _M_cur_results;
365  }
366  }
367  }
368  }
369  else
370  {
371  if (_M_current == _M_begin
372  && (_M_flags & regex_constants::match_not_null))
373  break;
374  if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end)
375  if (!_M_has_sol)
376  {
377  _M_has_sol = true;
378  _M_results = _M_cur_results;
379  }
380  }
381  break;
382  case _S_opcode_alternative:
383  if (_M_nfa._M_flags & regex_constants::ECMAScript)
384  {
385  // TODO: Let BFS support ECMAScript's alternative operation.
386  _GLIBCXX_DEBUG_ASSERT(__dfs_mode);
387  _M_dfs(__match_mode, __state._M_alt);
388  // Pick lhs if it matches. Only try rhs if it doesn't.
389  if (!_M_has_sol)
390  _M_dfs(__match_mode, __state._M_next);
391  }
392  else
393  {
394  // Try both and compare the result.
395  // See "case _S_opcode_accept:" handling above.
396  _M_dfs(__match_mode, __state._M_alt);
397  auto __has_sol = _M_has_sol;
398  _M_has_sol = false;
399  _M_dfs(__match_mode, __state._M_next);
400  _M_has_sol |= __has_sol;
401  }
402  break;
403  default:
404  _GLIBCXX_DEBUG_ASSERT(false);
405  }
406  }
407 
408  // Return whether now is at some word boundary.
409  template<typename _BiIter, typename _Alloc, typename _TraitsT,
410  bool __dfs_mode>
411  bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
412  _M_word_boundary() const
413  {
414  bool __left_is_word = false;
415  if (_M_current != _M_begin
416  || (_M_flags & regex_constants::match_prev_avail))
417  {
418  auto __prev = _M_current;
419  if (_M_is_word(*std::prev(__prev)))
420  __left_is_word = true;
421  }
422  bool __right_is_word =
423  _M_current != _M_end && _M_is_word(*_M_current);
424 
425  if (__left_is_word == __right_is_word)
426  return false;
427  if (__left_is_word && !(_M_flags & regex_constants::match_not_eow))
428  return true;
429  if (__right_is_word && !(_M_flags & regex_constants::match_not_bow))
430  return true;
431  return false;
432  }
433 
434 _GLIBCXX_END_NAMESPACE_VERSION
435 } // namespace __detail
436 } // namespace