libstdc++
|
00001 // class template regex -*- C++ -*- 00002 00003 // Copyright (C) 2013-2014 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_flags & regex_constants::match_continuous) 00043 return _M_search_from_first(); 00044 auto __cur = _M_begin; 00045 do 00046 { 00047 _M_current = __cur; 00048 if (_M_main<false>()) 00049 return true; 00050 } 00051 // Continue when __cur == _M_end 00052 while (__cur++ != _M_end); 00053 return false; 00054 } 00055 00056 // This function operates in different modes, DFS mode or BFS mode, indicated 00057 // by template parameter __dfs_mode. See _M_main for details. 00058 // 00059 // ------------------------------------------------------------ 00060 // 00061 // DFS mode: 00062 // 00063 // It applies a Depth-First-Search (aka backtracking) on given NFA and input 00064 // string. 00065 // At the very beginning the executor stands in the start state, then it tries 00066 // every possible state transition in current state recursively. Some state 00067 // transitions consume input string, say, a single-char-matcher or a 00068 // back-reference matcher; some don't, like assertion or other anchor nodes. 00069 // When the input is exhausted and/or the current state is an accepting state, 00070 // the whole executor returns true. 00071 // 00072 // TODO: This approach is exponentially slow for certain input. 00073 // Try to compile the NFA to a DFA. 00074 // 00075 // Time complexity: \Omega(match_length), O(2^(_M_nfa.size())) 00076 // Space complexity: \theta(match_results.size() + match_length) 00077 // 00078 // ------------------------------------------------------------ 00079 // 00080 // BFS mode: 00081 // 00082 // Russ Cox's article (http://swtch.com/~rsc/regexp/regexp1.html) 00083 // explained this algorithm clearly. 00084 // 00085 // It first computes epsilon closure (states that can be achieved without 00086 // consuming characters) for every state that's still matching, 00087 // using the same DFS algorithm, but doesn't re-enter states (find a true in 00088 // _M_visited), nor follows _S_opcode_match. 00089 // 00090 // Then apply DFS using every _S_opcode_match (in _M_match_queue) as the start 00091 // state. 00092 // 00093 // It significantly reduces potential duplicate states, so has a better 00094 // upper bound; but it requires more overhead. 00095 // 00096 // Time complexity: \Omega(match_length * match_results.size()) 00097 // O(match_length * _M_nfa.size() * match_results.size()) 00098 // Space complexity: \Omega(_M_nfa.size() + match_results.size()) 00099 // O(_M_nfa.size() * match_results.size()) 00100 template<typename _BiIter, typename _Alloc, typename _TraitsT, 00101 bool __dfs_mode> 00102 template<bool __match_mode> 00103 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 00104 _M_main() 00105 { 00106 if (__dfs_mode) 00107 { 00108 _M_has_sol = false; 00109 _M_cur_results = _M_results; 00110 _M_dfs<__match_mode>(_M_start_state); 00111 return _M_has_sol; 00112 } 00113 else 00114 { 00115 _M_match_queue->push_back(make_pair(_M_start_state, _M_results)); 00116 bool __ret = false; 00117 while (1) 00118 { 00119 _M_has_sol = false; 00120 if (_M_match_queue->empty()) 00121 break; 00122 _M_visited->assign(_M_visited->size(), false); 00123 auto __old_queue = std::move(*_M_match_queue); 00124 for (auto& __task : __old_queue) 00125 { 00126 _M_cur_results = std::move(__task.second); 00127 _M_dfs<__match_mode>(__task.first); 00128 } 00129 if (!__match_mode) 00130 __ret |= _M_has_sol; 00131 if (_M_current == _M_end) 00132 break; 00133 ++_M_current; 00134 } 00135 if (__match_mode) 00136 __ret = _M_has_sol; 00137 return __ret; 00138 } 00139 } 00140 00141 // Return whether now match the given sub-NFA. 00142 template<typename _BiIter, typename _Alloc, typename _TraitsT, 00143 bool __dfs_mode> 00144 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 00145 _M_lookahead(_State<_TraitsT> __state) 00146 { 00147 _ResultsVec __what(_M_cur_results.size()); 00148 auto __sub = std::unique_ptr<_Executor>(new _Executor(_M_current, 00149 _M_end, 00150 __what, 00151 _M_re, 00152 _M_flags)); 00153 __sub->_M_start_state = __state._M_alt; 00154 if (__sub->_M_search_from_first()) 00155 { 00156 for (size_t __i = 0; __i < __what.size(); __i++) 00157 if (__what[__i].matched) 00158 _M_cur_results[__i] = __what[__i]; 00159 return true; 00160 } 00161 return false; 00162 } 00163 00164 // TODO: Use a function vector to dispatch, instead of using switch-case. 00165 template<typename _BiIter, typename _Alloc, typename _TraitsT, 00166 bool __dfs_mode> 00167 template<bool __match_mode> 00168 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 00169 _M_dfs(_StateIdT __i) 00170 { 00171 if (!__dfs_mode) 00172 { 00173 if ((*_M_visited)[__i]) 00174 return; 00175 (*_M_visited)[__i] = true; 00176 } 00177 00178 const auto& __state = _M_nfa[__i]; 00179 // Every change on _M_cur_results and _M_current will be rolled back after 00180 // finishing the recursion step. 00181 switch (__state._M_opcode) 00182 { 00183 // _M_alt branch is "match once more", while _M_next is "get me out 00184 // of this quantifier". Executing _M_next first or _M_alt first don't 00185 // mean the same thing, and we need to choose the correct order under 00186 // given greedy mode. 00187 case _S_opcode_alternative: 00188 // Greedy. 00189 if (!__state._M_neg) 00190 { 00191 // "Once more" is preferred in greedy mode. 00192 _M_dfs<__match_mode>(__state._M_alt); 00193 // If it's DFS executor and already accepted, we're done. 00194 if (!__dfs_mode || !_M_has_sol) 00195 _M_dfs<__match_mode>(__state._M_next); 00196 } 00197 else // Non-greedy mode 00198 { 00199 if (__dfs_mode) 00200 { 00201 // vice-versa. 00202 _M_dfs<__match_mode>(__state._M_next); 00203 if (!_M_has_sol) 00204 _M_dfs<__match_mode>(__state._M_alt); 00205 } 00206 else 00207 { 00208 // DON'T attempt anything, because there's already another 00209 // state with higher priority accepted. This state cannot be 00210 // better by attempting its next node. 00211 if (!_M_has_sol) 00212 { 00213 _M_dfs<__match_mode>(__state._M_next); 00214 // DON'T attempt anything if it's already accepted. An 00215 // accepted state *must* be better than a solution that 00216 // matches a non-greedy quantifier one more time. 00217 if (!_M_has_sol) 00218 _M_dfs<__match_mode>(__state._M_alt); 00219 } 00220 } 00221 } 00222 break; 00223 case _S_opcode_subexpr_begin: 00224 // If there's nothing changed since last visit, do NOT continue. 00225 // This prevents the executor from get into infinite loop when using 00226 // "()*" to match "". 00227 if (!_M_cur_results[__state._M_subexpr].matched 00228 || _M_cur_results[__state._M_subexpr].first != _M_current) 00229 { 00230 auto& __res = _M_cur_results[__state._M_subexpr]; 00231 auto __back = __res.first; 00232 __res.first = _M_current; 00233 _M_dfs<__match_mode>(__state._M_next); 00234 __res.first = __back; 00235 } 00236 break; 00237 case _S_opcode_subexpr_end: 00238 if (_M_cur_results[__state._M_subexpr].second != _M_current 00239 || _M_cur_results[__state._M_subexpr].matched != true) 00240 { 00241 auto& __res = _M_cur_results[__state._M_subexpr]; 00242 auto __back = __res; 00243 __res.second = _M_current; 00244 __res.matched = true; 00245 _M_dfs<__match_mode>(__state._M_next); 00246 __res = __back; 00247 } 00248 else 00249 _M_dfs<__match_mode>(__state._M_next); 00250 break; 00251 case _S_opcode_line_begin_assertion: 00252 if (_M_at_begin()) 00253 _M_dfs<__match_mode>(__state._M_next); 00254 break; 00255 case _S_opcode_line_end_assertion: 00256 if (_M_at_end()) 00257 _M_dfs<__match_mode>(__state._M_next); 00258 break; 00259 case _S_opcode_word_boundary: 00260 if (_M_word_boundary(__state) == !__state._M_neg) 00261 _M_dfs<__match_mode>(__state._M_next); 00262 break; 00263 // Here __state._M_alt offers a single start node for a sub-NFA. 00264 // We recursively invoke our algorithm to match the sub-NFA. 00265 case _S_opcode_subexpr_lookahead: 00266 if (_M_lookahead(__state) == !__state._M_neg) 00267 _M_dfs<__match_mode>(__state._M_next); 00268 break; 00269 case _S_opcode_match: 00270 if (_M_current == _M_end) 00271 break; 00272 if (__dfs_mode) 00273 { 00274 if (__state._M_matches(*_M_current)) 00275 { 00276 ++_M_current; 00277 _M_dfs<__match_mode>(__state._M_next); 00278 --_M_current; 00279 } 00280 } 00281 else 00282 if (__state._M_matches(*_M_current)) 00283 _M_match_queue->push_back(make_pair(__state._M_next, 00284 _M_cur_results)); 00285 break; 00286 // First fetch the matched result from _M_cur_results as __submatch; 00287 // then compare it with 00288 // (_M_current, _M_current + (__submatch.second - __submatch.first)). 00289 // If matched, keep going; else just return and try another state. 00290 case _S_opcode_backref: 00291 { 00292 _GLIBCXX_DEBUG_ASSERT(__dfs_mode); 00293 auto& __submatch = _M_cur_results[__state._M_backref_index]; 00294 if (!__submatch.matched) 00295 break; 00296 auto __last = _M_current; 00297 for (auto __tmp = __submatch.first; 00298 __last != _M_end && __tmp != __submatch.second; 00299 ++__tmp) 00300 ++__last; 00301 if (_M_re._M_traits.transform(__submatch.first, 00302 __submatch.second) 00303 == _M_re._M_traits.transform(_M_current, __last)) 00304 { 00305 if (__last != _M_current) 00306 { 00307 auto __backup = _M_current; 00308 _M_current = __last; 00309 _M_dfs<__match_mode>(__state._M_next); 00310 _M_current = __backup; 00311 } 00312 else 00313 _M_dfs<__match_mode>(__state._M_next); 00314 } 00315 } 00316 break; 00317 case _S_opcode_accept: 00318 if (__dfs_mode) 00319 { 00320 _GLIBCXX_DEBUG_ASSERT(!_M_has_sol); 00321 if (__match_mode) 00322 _M_has_sol = _M_current == _M_end; 00323 else 00324 _M_has_sol = true; 00325 if (_M_current == _M_begin 00326 && (_M_flags & regex_constants::match_not_null)) 00327 _M_has_sol = false; 00328 if (_M_has_sol) 00329 _M_results = _M_cur_results; 00330 } 00331 else 00332 { 00333 if (_M_current == _M_begin 00334 && (_M_flags & regex_constants::match_not_null)) 00335 break; 00336 if (!__match_mode || _M_current == _M_end) 00337 if (!_M_has_sol) 00338 { 00339 _M_has_sol = true; 00340 _M_results = _M_cur_results; 00341 } 00342 } 00343 break; 00344 default: 00345 _GLIBCXX_DEBUG_ASSERT(false); 00346 } 00347 } 00348 00349 // Return whether now is at some word boundary. 00350 template<typename _BiIter, typename _Alloc, typename _TraitsT, 00351 bool __dfs_mode> 00352 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 00353 _M_word_boundary(_State<_TraitsT> __state) const 00354 { 00355 bool __left_is_word = false; 00356 if (_M_current != _M_begin 00357 || (_M_flags & regex_constants::match_prev_avail)) 00358 { 00359 auto __prev = _M_current; 00360 if (_M_is_word(*std::prev(__prev))) 00361 __left_is_word = true; 00362 } 00363 bool __right_is_word = 00364 _M_current != _M_end && _M_is_word(*_M_current); 00365 00366 if (__left_is_word == __right_is_word) 00367 return false; 00368 if (__left_is_word && !(_M_flags & regex_constants::match_not_eow)) 00369 return true; 00370 if (__right_is_word && !(_M_flags & regex_constants::match_not_bow)) 00371 return true; 00372 return false; 00373 } 00374 00375 _GLIBCXX_END_NAMESPACE_VERSION 00376 } // namespace __detail 00377 } // namespace