libstdc++
regex_executor.tcc
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00001 // class template regex -*- C++ -*-
00002 
00003 // Copyright (C) 2013-2019 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 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00034 
00035 namespace __detail
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(_StateIdT __next)
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 = __next;
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   // _M_alt branch is "match once more", while _M_next is "get me out
00199   // of this quantifier". Executing _M_next first or _M_alt first don't
00200   // mean the same thing, and we need to choose the correct order under
00201   // given greedy mode.
00202   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00203            bool __dfs_mode>
00204     void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00205     _M_handle_repeat(_Match_mode __match_mode, _StateIdT __i)
00206     {
00207       const auto& __state = _M_nfa[__i];
00208 
00209       // Greedy.
00210       if (!__state._M_neg)
00211         {
00212           _M_rep_once_more(__match_mode, __i);
00213           // If it's DFS executor and already accepted, we're done.
00214           if (!__dfs_mode || !_M_has_sol)
00215             _M_dfs(__match_mode, __state._M_next);
00216         }
00217       else // Non-greedy mode
00218         {
00219           if (__dfs_mode)
00220             {
00221               // vice-versa.
00222               _M_dfs(__match_mode, __state._M_next);
00223               if (!_M_has_sol)
00224                 _M_rep_once_more(__match_mode, __i);
00225             }
00226           else
00227             {
00228               // DON'T attempt anything, because there's already another
00229               // state with higher priority accepted. This state cannot
00230               // be better by attempting its next node.
00231               if (!_M_has_sol)
00232                 {
00233                   _M_dfs(__match_mode, __state._M_next);
00234                   // DON'T attempt anything if it's already accepted. An
00235                   // accepted state *must* be better than a solution that
00236                   // matches a non-greedy quantifier one more time.
00237                   if (!_M_has_sol)
00238                     _M_rep_once_more(__match_mode, __i);
00239                 }
00240             }
00241         }
00242     }
00243 
00244   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00245            bool __dfs_mode>
00246     void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00247     _M_handle_subexpr_begin(_Match_mode __match_mode, _StateIdT __i)
00248     {
00249       const auto& __state = _M_nfa[__i];
00250 
00251       auto& __res = _M_cur_results[__state._M_subexpr];
00252       auto __back = __res.first;
00253       __res.first = _M_current;
00254       _M_dfs(__match_mode, __state._M_next);
00255       __res.first = __back;
00256     }
00257 
00258   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00259            bool __dfs_mode>
00260     void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00261     _M_handle_subexpr_end(_Match_mode __match_mode, _StateIdT __i)
00262     {
00263       const auto& __state = _M_nfa[__i];
00264 
00265       auto& __res = _M_cur_results[__state._M_subexpr];
00266       auto __back = __res;
00267       __res.second = _M_current;
00268       __res.matched = true;
00269       _M_dfs(__match_mode, __state._M_next);
00270       __res = __back;
00271     }
00272 
00273   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00274            bool __dfs_mode>
00275     inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00276     _M_handle_line_begin_assertion(_Match_mode __match_mode, _StateIdT __i)
00277     {
00278       const auto& __state = _M_nfa[__i];
00279       if (_M_at_begin())
00280         _M_dfs(__match_mode, __state._M_next);
00281     }
00282 
00283   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00284            bool __dfs_mode>
00285     inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00286     _M_handle_line_end_assertion(_Match_mode __match_mode, _StateIdT __i)
00287     {
00288       const auto& __state = _M_nfa[__i];
00289       if (_M_at_end())
00290         _M_dfs(__match_mode, __state._M_next);
00291     }
00292 
00293   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00294            bool __dfs_mode>
00295     inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00296     _M_handle_word_boundary(_Match_mode __match_mode, _StateIdT __i)
00297     {
00298       const auto& __state = _M_nfa[__i];
00299       if (_M_word_boundary() == !__state._M_neg)
00300         _M_dfs(__match_mode, __state._M_next);
00301     }
00302 
00303   // Here __state._M_alt offers a single start node for a sub-NFA.
00304   // We recursively invoke our algorithm to match the sub-NFA.
00305   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00306            bool __dfs_mode>
00307     void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00308     _M_handle_subexpr_lookahead(_Match_mode __match_mode, _StateIdT __i)
00309     {
00310       const auto& __state = _M_nfa[__i];
00311       if (_M_lookahead(__state._M_alt) == !__state._M_neg)
00312         _M_dfs(__match_mode, __state._M_next);
00313     }
00314 
00315   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00316            bool __dfs_mode>
00317     void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00318     _M_handle_match(_Match_mode __match_mode, _StateIdT __i)
00319     {
00320       const auto& __state = _M_nfa[__i];
00321 
00322       if (_M_current == _M_end)
00323         return;
00324       if (__dfs_mode)
00325         {
00326           if (__state._M_matches(*_M_current))
00327             {
00328               ++_M_current;
00329               _M_dfs(__match_mode, __state._M_next);
00330               --_M_current;
00331             }
00332         }
00333       else
00334         if (__state._M_matches(*_M_current))
00335           _M_states._M_queue(__state._M_next, _M_cur_results);
00336     }
00337 
00338   template<typename _BiIter, typename _TraitsT>
00339     struct _Backref_matcher
00340     {
00341       _Backref_matcher(bool __icase, const _TraitsT& __traits)
00342       : _M_traits(__traits) { }
00343 
00344       bool
00345       _M_apply(_BiIter __expected_begin,
00346                _BiIter __expected_end, _BiIter __actual_begin,
00347                _BiIter __actual_end)
00348       {
00349         return _M_traits.transform(__expected_begin, __expected_end)
00350             == _M_traits.transform(__actual_begin, __actual_end);
00351       }
00352 
00353       const _TraitsT& _M_traits;
00354     };
00355 
00356   template<typename _BiIter, typename _CharT>
00357     struct _Backref_matcher<_BiIter, std::regex_traits<_CharT>>
00358     {
00359       using _TraitsT = std::regex_traits<_CharT>;
00360       _Backref_matcher(bool __icase, const _TraitsT& __traits)
00361       : _M_icase(__icase), _M_traits(__traits) { }
00362 
00363       bool
00364       _M_apply(_BiIter __expected_begin,
00365                _BiIter __expected_end, _BiIter __actual_begin,
00366                _BiIter __actual_end)
00367       {
00368         if (!_M_icase)
00369           return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end,
00370                                __actual_begin, __actual_end);
00371         typedef std::ctype<_CharT> __ctype_type;
00372         const auto& __fctyp = use_facet<__ctype_type>(_M_traits.getloc());
00373         return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end,
00374                              __actual_begin, __actual_end,
00375                              [this, &__fctyp](_CharT __lhs, _CharT __rhs)
00376                              {
00377                                return __fctyp.tolower(__lhs)
00378                                  == __fctyp.tolower(__rhs);
00379                              });
00380       }
00381 
00382       bool _M_icase;
00383       const _TraitsT& _M_traits;
00384     };
00385 
00386   // First fetch the matched result from _M_cur_results as __submatch;
00387   // then compare it with
00388   // (_M_current, _M_current + (__submatch.second - __submatch.first)).
00389   // If matched, keep going; else just return and try another state.
00390   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00391            bool __dfs_mode>
00392     void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00393     _M_handle_backref(_Match_mode __match_mode, _StateIdT __i)
00394     {
00395       __glibcxx_assert(__dfs_mode);
00396 
00397       const auto& __state = _M_nfa[__i];
00398       auto& __submatch = _M_cur_results[__state._M_backref_index];
00399       if (!__submatch.matched)
00400         return;
00401       auto __last = _M_current;
00402       for (auto __tmp = __submatch.first;
00403            __last != _M_end && __tmp != __submatch.second;
00404            ++__tmp)
00405         ++__last;
00406       if (_Backref_matcher<_BiIter, _TraitsT>(
00407               _M_re.flags() & regex_constants::icase,
00408               _M_re._M_automaton->_M_traits)._M_apply(
00409                   __submatch.first, __submatch.second, _M_current, __last))
00410         {
00411           if (__last != _M_current)
00412             {
00413               auto __backup = _M_current;
00414               _M_current = __last;
00415               _M_dfs(__match_mode, __state._M_next);
00416               _M_current = __backup;
00417             }
00418           else
00419             _M_dfs(__match_mode, __state._M_next);
00420         }
00421     }
00422 
00423   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00424            bool __dfs_mode>
00425     void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00426     _M_handle_accept(_Match_mode __match_mode, _StateIdT __i)
00427     {
00428       if (__dfs_mode)
00429         {
00430           __glibcxx_assert(!_M_has_sol);
00431           if (__match_mode == _Match_mode::_Exact)
00432             _M_has_sol = _M_current == _M_end;
00433           else
00434             _M_has_sol = true;
00435           if (_M_current == _M_begin
00436               && (_M_flags & regex_constants::match_not_null))
00437             _M_has_sol = false;
00438           if (_M_has_sol)
00439             {
00440               if (_M_nfa._M_flags & regex_constants::ECMAScript)
00441                 _M_results = _M_cur_results;
00442               else // POSIX
00443                 {
00444                   __glibcxx_assert(_M_states._M_get_sol_pos());
00445                   // Here's POSIX's logic: match the longest one. However
00446                   // we never know which one (lhs or rhs of "|") is longer
00447                   // unless we try both of them and compare the results.
00448                   // The member variable _M_sol_pos records the end
00449                   // position of the last successful match. It's better
00450                   // to be larger, because POSIX regex is always greedy.
00451                   // TODO: This could be slow.
00452                   if (*_M_states._M_get_sol_pos() == _BiIter()
00453                       || std::distance(_M_begin,
00454                                        *_M_states._M_get_sol_pos())
00455                          < std::distance(_M_begin, _M_current))
00456                     {
00457                       *_M_states._M_get_sol_pos() = _M_current;
00458                       _M_results = _M_cur_results;
00459                     }
00460                 }
00461             }
00462         }
00463       else
00464         {
00465           if (_M_current == _M_begin
00466               && (_M_flags & regex_constants::match_not_null))
00467             return;
00468           if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end)
00469             if (!_M_has_sol)
00470               {
00471                 _M_has_sol = true;
00472                 _M_results = _M_cur_results;
00473               }
00474         }
00475     }
00476 
00477   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00478            bool __dfs_mode>
00479     void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00480     _M_handle_alternative(_Match_mode __match_mode, _StateIdT __i)
00481     {
00482       const auto& __state = _M_nfa[__i];
00483 
00484       if (_M_nfa._M_flags & regex_constants::ECMAScript)
00485         {
00486           // TODO: Fix BFS support. It is wrong.
00487           _M_dfs(__match_mode, __state._M_alt);
00488           // Pick lhs if it matches. Only try rhs if it doesn't.
00489           if (!_M_has_sol)
00490             _M_dfs(__match_mode, __state._M_next);
00491         }
00492       else
00493         {
00494           // Try both and compare the result.
00495           // See "case _S_opcode_accept:" handling above.
00496           _M_dfs(__match_mode, __state._M_alt);
00497           auto __has_sol = _M_has_sol;
00498           _M_has_sol = false;
00499           _M_dfs(__match_mode, __state._M_next);
00500           _M_has_sol |= __has_sol;
00501         }
00502     }
00503 
00504   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00505            bool __dfs_mode>
00506     void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00507     _M_dfs(_Match_mode __match_mode, _StateIdT __i)
00508     {
00509       if (_M_states._M_visited(__i))
00510         return;
00511 
00512       switch (_M_nfa[__i]._M_opcode())
00513         {
00514         case _S_opcode_repeat:
00515           _M_handle_repeat(__match_mode, __i); break;
00516         case _S_opcode_subexpr_begin:
00517           _M_handle_subexpr_begin(__match_mode, __i); break;
00518         case _S_opcode_subexpr_end:
00519           _M_handle_subexpr_end(__match_mode, __i); break;
00520         case _S_opcode_line_begin_assertion:
00521           _M_handle_line_begin_assertion(__match_mode, __i); break;
00522         case _S_opcode_line_end_assertion:
00523           _M_handle_line_end_assertion(__match_mode, __i); break;
00524         case _S_opcode_word_boundary:
00525           _M_handle_word_boundary(__match_mode, __i); break;
00526         case _S_opcode_subexpr_lookahead:
00527           _M_handle_subexpr_lookahead(__match_mode, __i); break;
00528         case _S_opcode_match:
00529           _M_handle_match(__match_mode, __i); break;
00530         case _S_opcode_backref:
00531           _M_handle_backref(__match_mode, __i); break;
00532         case _S_opcode_accept:
00533           _M_handle_accept(__match_mode, __i); break;
00534         case _S_opcode_alternative:
00535           _M_handle_alternative(__match_mode, __i); break;
00536         default:
00537           __glibcxx_assert(false);
00538         }
00539     }
00540 
00541   // Return whether now is at some word boundary.
00542   template<typename _BiIter, typename _Alloc, typename _TraitsT,
00543            bool __dfs_mode>
00544     bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
00545     _M_word_boundary() const
00546     {
00547       if (_M_current == _M_begin && (_M_flags & regex_constants::match_not_bow))
00548         return false;
00549       if (_M_current == _M_end && (_M_flags & regex_constants::match_not_eow))
00550         return false;
00551 
00552       bool __left_is_word = false;
00553       if (_M_current != _M_begin
00554           || (_M_flags & regex_constants::match_prev_avail))
00555         {
00556           auto __prev = _M_current;
00557           if (_M_is_word(*std::prev(__prev)))
00558             __left_is_word = true;
00559         }
00560       bool __right_is_word =
00561         _M_current != _M_end && _M_is_word(*_M_current);
00562 
00563       return __left_is_word != __right_is_word;
00564     }
00565 } // namespace __detail
00566 
00567 _GLIBCXX_END_NAMESPACE_VERSION
00568 } // namespace