libstdc++
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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 // Backreferences may refer to captured content. 00148 // We may want to make this faster by not copying, 00149 // but let's not be clever prematurely. 00150 _ResultsVec __what(_M_cur_results); 00151 auto __sub = std::unique_ptr<_Executor>(new _Executor(_M_current, 00152 _M_end, 00153 __what, 00154 _M_re, 00155 _M_flags)); 00156 __sub->_M_start_state = __state._M_alt; 00157 if (__sub->_M_search_from_first()) 00158 { 00159 for (size_t __i = 0; __i < __what.size(); __i++) 00160 if (__what[__i].matched) 00161 _M_cur_results[__i] = __what[__i]; 00162 return true; 00163 } 00164 return false; 00165 } 00166 00167 // TODO: Use a function vector to dispatch, instead of using switch-case. 00168 template<typename _BiIter, typename _Alloc, typename _TraitsT, 00169 bool __dfs_mode> 00170 template<bool __match_mode> 00171 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 00172 _M_dfs(_StateIdT __i) 00173 { 00174 if (!__dfs_mode) 00175 { 00176 if ((*_M_visited)[__i]) 00177 return; 00178 (*_M_visited)[__i] = true; 00179 } 00180 00181 const auto& __state = _M_nfa[__i]; 00182 // Every change on _M_cur_results and _M_current will be rolled back after 00183 // finishing the recursion step. 00184 switch (__state._M_opcode) 00185 { 00186 // _M_alt branch is "match once more", while _M_next is "get me out 00187 // of this quantifier". Executing _M_next first or _M_alt first don't 00188 // mean the same thing, and we need to choose the correct order under 00189 // given greedy mode. 00190 case _S_opcode_alternative: 00191 // Greedy. 00192 if (!__state._M_neg) 00193 { 00194 // "Once more" is preferred in greedy mode. 00195 _M_dfs<__match_mode>(__state._M_alt); 00196 // If it's DFS executor and already accepted, we're done. 00197 if (!__dfs_mode || !_M_has_sol) 00198 _M_dfs<__match_mode>(__state._M_next); 00199 } 00200 else // Non-greedy mode 00201 { 00202 if (__dfs_mode) 00203 { 00204 // vice-versa. 00205 _M_dfs<__match_mode>(__state._M_next); 00206 if (!_M_has_sol) 00207 _M_dfs<__match_mode>(__state._M_alt); 00208 } 00209 else 00210 { 00211 // DON'T attempt anything, because there's already another 00212 // state with higher priority accepted. This state cannot be 00213 // better by attempting its next node. 00214 if (!_M_has_sol) 00215 { 00216 _M_dfs<__match_mode>(__state._M_next); 00217 // DON'T attempt anything if it's already accepted. An 00218 // accepted state *must* be better than a solution that 00219 // matches a non-greedy quantifier one more time. 00220 if (!_M_has_sol) 00221 _M_dfs<__match_mode>(__state._M_alt); 00222 } 00223 } 00224 } 00225 break; 00226 case _S_opcode_subexpr_begin: 00227 // If there's nothing changed since last visit, do NOT continue. 00228 // This prevents the executor from get into infinite loop when using 00229 // "()*" to match "". 00230 if (!_M_cur_results[__state._M_subexpr].matched 00231 || _M_cur_results[__state._M_subexpr].first != _M_current) 00232 { 00233 auto& __res = _M_cur_results[__state._M_subexpr]; 00234 auto __back = __res.first; 00235 __res.first = _M_current; 00236 _M_dfs<__match_mode>(__state._M_next); 00237 __res.first = __back; 00238 } 00239 break; 00240 case _S_opcode_subexpr_end: 00241 if (_M_cur_results[__state._M_subexpr].second != _M_current 00242 || _M_cur_results[__state._M_subexpr].matched != true) 00243 { 00244 auto& __res = _M_cur_results[__state._M_subexpr]; 00245 auto __back = __res; 00246 __res.second = _M_current; 00247 __res.matched = true; 00248 _M_dfs<__match_mode>(__state._M_next); 00249 __res = __back; 00250 } 00251 else 00252 _M_dfs<__match_mode>(__state._M_next); 00253 break; 00254 case _S_opcode_line_begin_assertion: 00255 if (_M_at_begin()) 00256 _M_dfs<__match_mode>(__state._M_next); 00257 break; 00258 case _S_opcode_line_end_assertion: 00259 if (_M_at_end()) 00260 _M_dfs<__match_mode>(__state._M_next); 00261 break; 00262 case _S_opcode_word_boundary: 00263 if (_M_word_boundary(__state) == !__state._M_neg) 00264 _M_dfs<__match_mode>(__state._M_next); 00265 break; 00266 // Here __state._M_alt offers a single start node for a sub-NFA. 00267 // We recursively invoke our algorithm to match the sub-NFA. 00268 case _S_opcode_subexpr_lookahead: 00269 if (_M_lookahead(__state) == !__state._M_neg) 00270 _M_dfs<__match_mode>(__state._M_next); 00271 break; 00272 case _S_opcode_match: 00273 if (_M_current == _M_end) 00274 break; 00275 if (__dfs_mode) 00276 { 00277 if (__state._M_matches(*_M_current)) 00278 { 00279 ++_M_current; 00280 _M_dfs<__match_mode>(__state._M_next); 00281 --_M_current; 00282 } 00283 } 00284 else 00285 if (__state._M_matches(*_M_current)) 00286 _M_match_queue->push_back(make_pair(__state._M_next, 00287 _M_cur_results)); 00288 break; 00289 // First fetch the matched result from _M_cur_results as __submatch; 00290 // then compare it with 00291 // (_M_current, _M_current + (__submatch.second - __submatch.first)). 00292 // If matched, keep going; else just return and try another state. 00293 case _S_opcode_backref: 00294 { 00295 _GLIBCXX_DEBUG_ASSERT(__dfs_mode); 00296 auto& __submatch = _M_cur_results[__state._M_backref_index]; 00297 if (!__submatch.matched) 00298 break; 00299 auto __last = _M_current; 00300 for (auto __tmp = __submatch.first; 00301 __last != _M_end && __tmp != __submatch.second; 00302 ++__tmp) 00303 ++__last; 00304 if (_M_re._M_traits.transform(__submatch.first, 00305 __submatch.second) 00306 == _M_re._M_traits.transform(_M_current, __last)) 00307 { 00308 if (__last != _M_current) 00309 { 00310 auto __backup = _M_current; 00311 _M_current = __last; 00312 _M_dfs<__match_mode>(__state._M_next); 00313 _M_current = __backup; 00314 } 00315 else 00316 _M_dfs<__match_mode>(__state._M_next); 00317 } 00318 } 00319 break; 00320 case _S_opcode_accept: 00321 if (__dfs_mode) 00322 { 00323 _GLIBCXX_DEBUG_ASSERT(!_M_has_sol); 00324 if (__match_mode) 00325 _M_has_sol = _M_current == _M_end; 00326 else 00327 _M_has_sol = true; 00328 if (_M_current == _M_begin 00329 && (_M_flags & regex_constants::match_not_null)) 00330 _M_has_sol = false; 00331 if (_M_has_sol) 00332 _M_results = _M_cur_results; 00333 } 00334 else 00335 { 00336 if (_M_current == _M_begin 00337 && (_M_flags & regex_constants::match_not_null)) 00338 break; 00339 if (!__match_mode || _M_current == _M_end) 00340 if (!_M_has_sol) 00341 { 00342 _M_has_sol = true; 00343 _M_results = _M_cur_results; 00344 } 00345 } 00346 break; 00347 default: 00348 _GLIBCXX_DEBUG_ASSERT(false); 00349 } 00350 } 00351 00352 // Return whether now is at some word boundary. 00353 template<typename _BiIter, typename _Alloc, typename _TraitsT, 00354 bool __dfs_mode> 00355 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 00356 _M_word_boundary(_State<_TraitsT> __state) const 00357 { 00358 bool __left_is_word = false; 00359 if (_M_current != _M_begin 00360 || (_M_flags & regex_constants::match_prev_avail)) 00361 { 00362 auto __prev = _M_current; 00363 if (_M_is_word(*std::prev(__prev))) 00364 __left_is_word = true; 00365 } 00366 bool __right_is_word = 00367 _M_current != _M_end && _M_is_word(*_M_current); 00368 00369 if (__left_is_word == __right_is_word) 00370 return false; 00371 if (__left_is_word && !(_M_flags & regex_constants::match_not_eow)) 00372 return true; 00373 if (__right_is_word && !(_M_flags & regex_constants::match_not_bow)) 00374 return true; 00375 return false; 00376 } 00377 00378 _GLIBCXX_END_NAMESPACE_VERSION 00379 } // namespace __detail 00380 } // namespace