libstdc++
regex_executor.tcc
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00001 // class template regex -*- C++ -*-
00002 
00003 // Copyright (C) 2013-2015 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the
00007 // terms of the GNU General Public License as published by the
00008 // Free Software Foundation; either version 3, or (at your option)
00009 // any later version.
00010 
00011 // This library is distributed in the hope that it will be useful,
00012 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00014 // GNU General Public License for more details.
00015 
00016 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 /**
00026  *  @file bits/regex_executor.tcc
00027  *  This is an internal header file, included by other library headers.
00028  *  Do not attempt to use it directly. @headername{regex}
00029  */
00030 
00031 namespace std _GLIBCXX_VISIBILITY(default)
00032 {
00033 namespace __detail
00034 {
00035 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00036 
00037   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00038            bool __dfs_mode>
00039     bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00040     _M_search()
00041     {
00042       if (_M_search_from_first())
00043         return true;
00044       if (_M_flags & regex_constants::match_continuous)
00045         return false;
00046       _M_flags |= regex_constants::match_prev_avail;
00047       while (_M_begin != _M_end)
00048         {
00049           ++_M_begin;
00050           if (_M_search_from_first())
00051             return true;
00052         }
00053       return false;
00054     }
00055 
00056   // The _M_main function operates in different modes, DFS mode or BFS mode,
00057   // indicated by template parameter __dfs_mode, and dispatches to one of the
00058   // _M_main_dispatch overloads.
00059   //
00060   // ------------------------------------------------------------
00061   //
00062   // DFS mode:
00063   //
00064   // It applies a Depth-First-Search (aka backtracking) on given NFA and input
00065   // string.
00066   // At the very beginning the executor stands in the start state, then it
00067   // tries every possible state transition in current state recursively. Some
00068   // state transitions consume input string, say, a single-char-matcher or a
00069   // back-reference matcher; some don't, like assertion or other anchor nodes.
00070   // When the input is exhausted and/or the current state is an accepting
00071   // state, the whole executor returns true.
00072   //
00073   // TODO: This approach is exponentially slow for certain input.
00074   //       Try to compile the NFA to a DFA.
00075   //
00076   // Time complexity: \Omega(match_length), O(2^(_M_nfa.size()))
00077   // Space complexity: \theta(match_results.size() + match_length)
00078   //
00079   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00080            bool __dfs_mode>
00081     bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00082     _M_main_dispatch(_Match_mode __match_mode, __dfs)
00083     {
00084       _M_has_sol = false;
00085       *_M_states._M_get_sol_pos() = _BiIter();
00086       _M_cur_results = _M_results;
00087       _M_dfs(__match_mode, _M_states._M_start);
00088       return _M_has_sol;
00089     }
00090 
00091   // ------------------------------------------------------------
00092   //
00093   // BFS mode:
00094   //
00095   // Russ Cox's article (http://swtch.com/~rsc/regexp/regexp1.html)
00096   // explained this algorithm clearly.
00097   //
00098   // It first computes epsilon closure (states that can be achieved without
00099   // consuming characters) for every state that's still matching,
00100   // using the same DFS algorithm, but doesn't re-enter states (using
00101   // _M_states._M_visited to check), nor follow _S_opcode_match.
00102   //
00103   // Then apply DFS using every _S_opcode_match (in _M_states._M_match_queue)
00104   // as the start state.
00105   //
00106   // It significantly reduces potential duplicate states, so has a better
00107   // upper bound; but it requires more overhead.
00108   //
00109   // Time complexity: \Omega(match_length * match_results.size())
00110   //                  O(match_length * _M_nfa.size() * match_results.size())
00111   // Space complexity: \Omega(_M_nfa.size() + match_results.size())
00112   //                   O(_M_nfa.size() * match_results.size())
00113   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00114            bool __dfs_mode>
00115     bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00116     _M_main_dispatch(_Match_mode __match_mode, __bfs)
00117     {
00118       _M_states._M_queue(_M_states._M_start, _M_results);
00119       bool __ret = false;
00120       while (1)
00121         {
00122           _M_has_sol = false;
00123           if (_M_states._M_match_queue.empty())
00124             break;
00125           std::fill_n(_M_states._M_visited_states.get(), _M_nfa.size(), false);
00126           auto __old_queue = std::move(_M_states._M_match_queue);
00127           for (auto& __task : __old_queue)
00128             {
00129               _M_cur_results = std::move(__task.second);
00130               _M_dfs(__match_mode, __task.first);
00131             }
00132           if (__match_mode == _Match_mode::_Prefix)
00133             __ret |= _M_has_sol;
00134           if (_M_current == _M_end)
00135             break;
00136           ++_M_current;
00137         }
00138       if (__match_mode == _Match_mode::_Exact)
00139         __ret = _M_has_sol;
00140       _M_states._M_match_queue.clear();
00141       return __ret;
00142     }
00143 
00144   // Return whether now match the given sub-NFA.
00145   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00146            bool __dfs_mode>
00147     bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00148     _M_lookahead(_State<_TraitsT> __state)
00149     {
00150       // Backreferences may refer to captured content.
00151       // We may want to make this faster by not copying,
00152       // but let's not be clever prematurely.
00153       _ResultsVec __what(_M_cur_results);
00154       _Executor __sub(_M_current, _M_end, __what, _M_re, _M_flags);
00155       __sub._M_states._M_start = __state._M_alt;
00156       if (__sub._M_search_from_first())
00157         {
00158           for (size_t __i = 0; __i < __what.size(); __i++)
00159             if (__what[__i].matched)
00160               _M_cur_results[__i] = __what[__i];
00161           return true;
00162         }
00163       return false;
00164     }
00165 
00166   // __rep_count records how many times (__rep_count.second)
00167   // this node is visited under certain input iterator
00168   // (__rep_count.first). This prevent the executor from entering
00169   // infinite loop by refusing to continue when it's already been
00170   // visited more than twice. It's `twice` instead of `once` because
00171   // we need to spare one more time for potential group capture.
00172   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00173     bool __dfs_mode>
00174     void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00175     _M_rep_once_more(_Match_mode __match_mode, _StateIdT __i)
00176     {
00177       const auto& __state = _M_nfa[__i];
00178       auto& __rep_count = _M_rep_count[__i];
00179       if (__rep_count.second == 0 || __rep_count.first != _M_current)
00180         {
00181           auto __back = __rep_count;
00182           __rep_count.first = _M_current;
00183           __rep_count.second = 1;
00184           _M_dfs(__match_mode, __state._M_alt);
00185           __rep_count = __back;
00186         }
00187       else
00188         {
00189           if (__rep_count.second < 2)
00190             {
00191               __rep_count.second++;
00192               _M_dfs(__match_mode, __state._M_alt);
00193               __rep_count.second--;
00194             }
00195         }
00196     };
00197 
00198   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00199            bool __dfs_mode>
00200     void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00201     _M_dfs(_Match_mode __match_mode, _StateIdT __i)
00202     {
00203       if (_M_states._M_visited(__i))
00204         return;
00205 
00206       const auto& __state = _M_nfa[__i];
00207       // Every change on _M_cur_results and _M_current will be rolled back after
00208       // finishing the recursion step.
00209       switch (__state._M_opcode)
00210         {
00211         // _M_alt branch is "match once more", while _M_next is "get me out
00212         // of this quantifier". Executing _M_next first or _M_alt first don't
00213         // mean the same thing, and we need to choose the correct order under
00214         // given greedy mode.
00215         case _S_opcode_repeat:
00216           {
00217             // Greedy.
00218             if (!__state._M_neg)
00219               {
00220                 _M_rep_once_more(__match_mode, __i);
00221                 // If it's DFS executor and already accepted, we're done.
00222                 if (!__dfs_mode || !_M_has_sol)
00223                   _M_dfs(__match_mode, __state._M_next);
00224               }
00225             else // Non-greedy mode
00226               {
00227                 if (__dfs_mode)
00228                   {
00229                     // vice-versa.
00230                     _M_dfs(__match_mode, __state._M_next);
00231                     if (!_M_has_sol)
00232                       _M_rep_once_more(__match_mode, __i);
00233                   }
00234                 else
00235                   {
00236                     // DON'T attempt anything, because there's already another
00237                     // state with higher priority accepted. This state cannot
00238                     // be better by attempting its next node.
00239                     if (!_M_has_sol)
00240                       {
00241                         _M_dfs(__match_mode, __state._M_next);
00242                         // DON'T attempt anything if it's already accepted. An
00243                         // accepted state *must* be better than a solution that
00244                         // matches a non-greedy quantifier one more time.
00245                         if (!_M_has_sol)
00246                           _M_rep_once_more(__match_mode, __i);
00247                       }
00248                   }
00249               }
00250             }
00251           break;
00252         case _S_opcode_subexpr_begin:
00253           {
00254             auto& __res = _M_cur_results[__state._M_subexpr];
00255             auto __back = __res.first;
00256             __res.first = _M_current;
00257             _M_dfs(__match_mode, __state._M_next);
00258             __res.first = __back;
00259           }
00260           break;
00261         case _S_opcode_subexpr_end:
00262           {
00263             auto& __res = _M_cur_results[__state._M_subexpr];
00264             auto __back = __res;
00265             __res.second = _M_current;
00266             __res.matched = true;
00267             _M_dfs(__match_mode, __state._M_next);
00268             __res = __back;
00269           }
00270           break;
00271         case _S_opcode_line_begin_assertion:
00272           if (_M_at_begin())
00273             _M_dfs(__match_mode, __state._M_next);
00274           break;
00275         case _S_opcode_line_end_assertion:
00276           if (_M_at_end())
00277             _M_dfs(__match_mode, __state._M_next);
00278           break;
00279         case _S_opcode_word_boundary:
00280           if (_M_word_boundary() == !__state._M_neg)
00281             _M_dfs(__match_mode, __state._M_next);
00282           break;
00283         // Here __state._M_alt offers a single start node for a sub-NFA.
00284         // We recursively invoke our algorithm to match the sub-NFA.
00285         case _S_opcode_subexpr_lookahead:
00286           if (_M_lookahead(__state) == !__state._M_neg)
00287             _M_dfs(__match_mode, __state._M_next);
00288           break;
00289         case _S_opcode_match:
00290           if (_M_current == _M_end)
00291             break;
00292           if (__dfs_mode)
00293             {
00294               if (__state._M_matches(*_M_current))
00295                 {
00296                   ++_M_current;
00297                   _M_dfs(__match_mode, __state._M_next);
00298                   --_M_current;
00299                 }
00300             }
00301           else
00302             if (__state._M_matches(*_M_current))
00303               _M_states._M_queue(__state._M_next, _M_cur_results);
00304           break;
00305         // First fetch the matched result from _M_cur_results as __submatch;
00306         // then compare it with
00307         // (_M_current, _M_current + (__submatch.second - __submatch.first)).
00308         // If matched, keep going; else just return and try another state.
00309         case _S_opcode_backref:
00310           {
00311             _GLIBCXX_DEBUG_ASSERT(__dfs_mode);
00312             auto& __submatch = _M_cur_results[__state._M_backref_index];
00313             if (!__submatch.matched)
00314               break;
00315             auto __last = _M_current;
00316             for (auto __tmp = __submatch.first;
00317                  __last != _M_end && __tmp != __submatch.second;
00318                  ++__tmp)
00319               ++__last;
00320             if (_M_re._M_automaton->_M_traits.transform(__submatch.first,
00321                                                         __submatch.second)
00322                 == _M_re._M_automaton->_M_traits.transform(_M_current, __last))
00323               {
00324                 if (__last != _M_current)
00325                   {
00326                     auto __backup = _M_current;
00327                     _M_current = __last;
00328                     _M_dfs(__match_mode, __state._M_next);
00329                     _M_current = __backup;
00330                   }
00331                 else
00332                   _M_dfs(__match_mode, __state._M_next);
00333               }
00334           }
00335           break;
00336         case _S_opcode_accept:
00337           if (__dfs_mode)
00338             {
00339               _GLIBCXX_DEBUG_ASSERT(!_M_has_sol);
00340               if (__match_mode == _Match_mode::_Exact)
00341                 _M_has_sol = _M_current == _M_end;
00342               else
00343                 _M_has_sol = true;
00344               if (_M_current == _M_begin
00345                   && (_M_flags & regex_constants::match_not_null))
00346                 _M_has_sol = false;
00347               if (_M_has_sol)
00348                 {
00349                   if (_M_nfa._M_flags & regex_constants::ECMAScript)
00350                     _M_results = _M_cur_results;
00351                   else // POSIX
00352                     {
00353                       _GLIBCXX_DEBUG_ASSERT(_M_states._M_get_sol_pos());
00354                       // Here's POSIX's logic: match the longest one. However
00355                       // we never know which one (lhs or rhs of "|") is longer
00356                       // unless we try both of them and compare the results.
00357                       // The member variable _M_sol_pos records the end
00358                       // position of the last successful match. It's better
00359                       // to be larger, because POSIX regex is always greedy.
00360                       // TODO: This could be slow.
00361                       if (*_M_states._M_get_sol_pos() == _BiIter()
00362                           || std::distance(_M_begin,
00363                                            *_M_states._M_get_sol_pos())
00364                              < std::distance(_M_begin, _M_current))
00365                         {
00366                           *_M_states._M_get_sol_pos() = _M_current;
00367                           _M_results = _M_cur_results;
00368                         }
00369                     }
00370                 }
00371             }
00372           else
00373             {
00374               if (_M_current == _M_begin
00375                   && (_M_flags & regex_constants::match_not_null))
00376                 break;
00377               if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end)
00378                 if (!_M_has_sol)
00379                   {
00380                     _M_has_sol = true;
00381                     _M_results = _M_cur_results;
00382                   }
00383             }
00384           break;
00385         case _S_opcode_alternative:
00386           if (_M_nfa._M_flags & regex_constants::ECMAScript)
00387             {
00388               // TODO: Let BFS support ECMAScript's alternative operation.
00389               _GLIBCXX_DEBUG_ASSERT(__dfs_mode);
00390               _M_dfs(__match_mode, __state._M_alt);
00391               // Pick lhs if it matches. Only try rhs if it doesn't.
00392               if (!_M_has_sol)
00393                 _M_dfs(__match_mode, __state._M_next);
00394             }
00395           else
00396             {
00397               // Try both and compare the result.
00398               // See "case _S_opcode_accept:" handling above.
00399               _M_dfs(__match_mode, __state._M_alt);
00400               auto __has_sol = _M_has_sol;
00401               _M_has_sol = false;
00402               _M_dfs(__match_mode, __state._M_next);
00403               _M_has_sol |= __has_sol;
00404             }
00405           break;
00406         default:
00407           _GLIBCXX_DEBUG_ASSERT(false);
00408         }
00409     }
00410 
00411   // Return whether now is at some word boundary.
00412   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00413            bool __dfs_mode>
00414     bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00415     _M_word_boundary() const
00416     {
00417       bool __left_is_word = false;
00418       if (_M_current != _M_begin
00419           || (_M_flags & regex_constants::match_prev_avail))
00420         {
00421           auto __prev = _M_current;
00422           if (_M_is_word(*std::prev(__prev)))
00423             __left_is_word = true;
00424         }
00425       bool __right_is_word =
00426         _M_current != _M_end && _M_is_word(*_M_current);
00427 
00428       if (__left_is_word == __right_is_word)
00429         return false;
00430       if (__left_is_word && !(_M_flags & regex_constants::match_not_eow))
00431         return true;
00432       if (__right_is_word && !(_M_flags & regex_constants::match_not_bow))
00433         return true;
00434       return false;
00435     }
00436 
00437 _GLIBCXX_END_NAMESPACE_VERSION
00438 } // namespace __detail
00439 } // namespace