libstdc++-v3/include/bits/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(_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   template<typename _BiIter, typename _Alloc, typename _TraitsT,
 199            bool __dfs_mode>
 200     void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
 201     _M_dfs(_Match_mode __match_mode, _StateIdT __i)
 202     {
 203       if (_M_states._M_visited(__i))
 204         return;
 205
 206       const auto& __state = _M_nfa[__i];
 207       // Every change on _M_cur_results and _M_current will be rolled back after
 208       // finishing the recursion step.
 209       switch (__state._M_opcode())
 210         {
 211         // _M_alt branch is "match once more", while _M_next is "get me out
 212         // of this quantifier". Executing _M_next first or _M_alt first don't
 213         // mean the same thing, and we need to choose the correct order under
 214         // given greedy mode.
 215         case _S_opcode_repeat:
 216           {
 217             // Greedy.
 218             if (!__state._M_neg)
 219               {
 220                 _M_rep_once_more(__match_mode, __i);
 221                 // If it's DFS executor and already accepted, we're done.
 222                 if (!__dfs_mode || !_M_has_sol)
 223                   _M_dfs(__match_mode, __state._M_next);
 224               }
 225             else // Non-greedy mode
 226               {
 227                 if (__dfs_mode)
 228                   {
 229                     // vice-versa.
 230                     _M_dfs(__match_mode, __state._M_next);
 231                     if (!_M_has_sol)
 232                       _M_rep_once_more(__match_mode, __i);
 233                   }
 234                 else
 235                   {
 236                     // DON'T attempt anything, because there's already another
 237                     // state with higher priority accepted. This state cannot
 238                     // be better by attempting its next node.
 239                     if (!_M_has_sol)
 240                       {
 241                         _M_dfs(__match_mode, __state._M_next);
 242                         // DON'T attempt anything if it's already accepted. An
 243                         // accepted state *must* be better than a solution that
 244                         // matches a non-greedy quantifier one more time.
 245                         if (!_M_has_sol)
 246                           _M_rep_once_more(__match_mode, __i);
 247                       }
 248                   }
 249               }
 250             }
 251           break;
 252         case _S_opcode_subexpr_begin:
 253           {
 254             auto& __res = _M_cur_results[__state._M_subexpr];
 255             auto __back = __res.first;
 256             __res.first = _M_current;
 257             _M_dfs(__match_mode, __state._M_next);
 258             __res.first = __back;
 259           }
 260           break;
 261         case _S_opcode_subexpr_end:
 262           {
 263             auto& __res = _M_cur_results[__state._M_subexpr];
 264             auto __back = __res;
 265             __res.second = _M_current;
 266             __res.matched = true;
 267             _M_dfs(__match_mode, __state._M_next);
 268             __res = __back;
 269           }
 270           break;
 271         case _S_opcode_line_begin_assertion:
 272           if (_M_at_begin())
 273             _M_dfs(__match_mode, __state._M_next);
 274           break;
 275         case _S_opcode_line_end_assertion:
 276           if (_M_at_end())
 277             _M_dfs(__match_mode, __state._M_next);
 278           break;
 279         case _S_opcode_word_boundary:
 280           if (_M_word_boundary() == !__state._M_neg)
 281             _M_dfs(__match_mode, __state._M_next);
 282           break;
 283         // Here __state._M_alt offers a single start node for a sub-NFA.
 284         // We recursively invoke our algorithm to match the sub-NFA.
 285         case _S_opcode_subexpr_lookahead:
 286           if (_M_lookahead(__state._M_alt) == !__state._M_neg)
 287             _M_dfs(__match_mode, __state._M_next);
 288           break;
 289         case _S_opcode_match:
 290           if (_M_current == _M_end)
 291             break;
 292           if (__dfs_mode)
 293             {
 294               if (__state._M_matches(*_M_current))
 295                 {
 296                   ++_M_current;
 297                   _M_dfs(__match_mode, __state._M_next);
 298                   --_M_current;
 299                 }
 300             }
 301           else
 302             if (__state._M_matches(*_M_current))
 303               _M_states._M_queue(__state._M_next, _M_cur_results);
 304           break;
 305         // First fetch the matched result from _M_cur_results as __submatch;
 306         // then compare it with
 307         // (_M_current, _M_current + (__submatch.second - __submatch.first)).
 308         // If matched, keep going; else just return and try another state.
 309         case _S_opcode_backref:
 310           {
 311             __glibcxx_assert(__dfs_mode);
 312             auto& __submatch = _M_cur_results[__state._M_backref_index];
 313             if (!__submatch.matched)
 314               break;
 315             auto __last = _M_current;
 316             for (auto __tmp = __submatch.first;
 317                  __last != _M_end && __tmp != __submatch.second;
 318                  ++__tmp)
 319               ++__last;
 320             if (_M_re._M_automaton->_M_traits.transform(__submatch.first,
 321                                                         __submatch.second)
 322                 == _M_re._M_automaton->_M_traits.transform(_M_current, __last))
 323               {
 324                 if (__last != _M_current)
 325                   {
 326                     auto __backup = _M_current;
 327                     _M_current = __last;
 328                     _M_dfs(__match_mode, __state._M_next);
 329                     _M_current = __backup;
 330                   }
 331                 else
 332                   _M_dfs(__match_mode, __state._M_next);
 333               }
 334           }
 335           break;
 336         case _S_opcode_accept:
 337           if (__dfs_mode)
 338             {
 339               __glibcxx_assert(!_M_has_sol);
 340               if (__match_mode == _Match_mode::_Exact)
 341                 _M_has_sol = _M_current == _M_end;
 342               else
 343                 _M_has_sol = true;
 344               if (_M_current == _M_begin
 345                   && (_M_flags & regex_constants::match_not_null))
 346                 _M_has_sol = false;
 347               if (_M_has_sol)
 348                 {
 349                   if (_M_nfa._M_flags & regex_constants::ECMAScript)
 350                     _M_results = _M_cur_results;
 351                   else // POSIX
 352                     {
 353                       __glibcxx_assert(_M_states._M_get_sol_pos());
 354                       // Here's POSIX's logic: match the longest one. However
 355                       // we never know which one (lhs or rhs of "|") is longer
 356                       // unless we try both of them and compare the results.
 357                       // The member variable _M_sol_pos records the end
 358                       // position of the last successful match. It's better
 359                       // to be larger, because POSIX regex is always greedy.
 360                       // TODO: This could be slow.
 361                       if (*_M_states._M_get_sol_pos() == _BiIter()
 362                           || std::distance(_M_begin,
 363                                            *_M_states._M_get_sol_pos())
 364                              < std::distance(_M_begin, _M_current))
 365                         {
 366                           *_M_states._M_get_sol_pos() = _M_current;
 367                           _M_results = _M_cur_results;
 368                         }
 369                     }
 370                 }
 371             }
 372           else
 373             {
 374               if (_M_current == _M_begin
 375                   && (_M_flags & regex_constants::match_not_null))
 376                 break;
 377               if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end)
 378                 if (!_M_has_sol)
 379                   {
 380                     _M_has_sol = true;
 381                     _M_results = _M_cur_results;
 382                   }
 383             }
 384           break;
 385         case _S_opcode_alternative:
 386           if (_M_nfa._M_flags & regex_constants::ECMAScript)
 387             {
 388               // TODO: Fix BFS support. It is wrong.
 389               _M_dfs(__match_mode, __state._M_alt);
 390               // Pick lhs if it matches. Only try rhs if it doesn't.
 391               if (!_M_has_sol)
 392                 _M_dfs(__match_mode, __state._M_next);
 393             }
 394           else
 395             {
 396               // Try both and compare the result.
 397               // See "case _S_opcode_accept:" handling above.
 398               _M_dfs(__match_mode, __state._M_alt);
 399               auto __has_sol = _M_has_sol;
 400               _M_has_sol = false;
 401               _M_dfs(__match_mode, __state._M_next);
 402               _M_has_sol |= __has_sol;
 403             }
 404           break;
 405         default:
 406           __glibcxx_assert(false);
 407         }
 408     }
 409
 410   // Return whether now is at some word boundary.
 411   template<typename _BiIter, typename _Alloc, typename _TraitsT,
 412            bool __dfs_mode>
 413     bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
 414     _M_word_boundary() const
 415     {
 416       bool __left_is_word = false;
 417       if (_M_current != _M_begin
 418           || (_M_flags & regex_constants::match_prev_avail))
 419         {
 420           auto __prev = _M_current;
 421           if (_M_is_word(*std::prev(__prev)))
 422             __left_is_word = true;
 423         }
 424       bool __right_is_word =
 425         _M_current != _M_end && _M_is_word(*_M_current);
 426
 427       if (__left_is_word == __right_is_word)
 428         return false;
 429       if (__left_is_word && !(_M_flags & regex_constants::match_not_eow))
 430         return true;
 431       if (__right_is_word && !(_M_flags & regex_constants::match_not_bow))
 432         return true;
 433       return false;
 434     }
 435
 436 _GLIBCXX_END_NAMESPACE_VERSION
 437 } // namespace __detail
 438 } // namespace