1 // class template regex -*- C++ -*- 2 3 // Copyright (C) 2013-2014 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_flags & regex_constants::match_continuous) 43 return _M_search_from_first(); 44 auto __cur = _M_begin; 45 do 46 { 47 _M_current = __cur; 48 if (_M_main<false>()) 49 return true; 50 } 51 // Continue when __cur == _M_end 52 while (__cur++ != _M_end); 53 return false; 54 } 55 56 // This function operates in different modes, DFS mode or BFS mode, indicated 57 // by template parameter __dfs_mode. See _M_main for details. 58 // 59 // ------------------------------------------------------------ 60 // 61 // DFS mode: 62 // 63 // It applies a Depth-First-Search (aka backtracking) on given NFA and input 64 // string. 65 // At the very beginning the executor stands in the start state, then it tries 66 // every possible state transition in current state recursively. Some state 67 // transitions consume input string, say, a single-char-matcher or a 68 // back-reference matcher; some don't, like assertion or other anchor nodes. 69 // When the input is exhausted and/or the current state is an accepting state, 70 // the whole executor returns true. 71 // 72 // TODO: This approach is exponentially slow for certain input. 73 // Try to compile the NFA to a DFA. 74 // 75 // Time complexity: \Omega(match_length), O(2^(_M_nfa.size())) 76 // Space complexity: \theta(match_results.size() + match_length) 77 // 78 // ------------------------------------------------------------ 79 // 80 // BFS mode: 81 // 82 // Russ Cox's article (http://swtch.com/~rsc/regexp/regexp1.html) 83 // explained this algorithm clearly. 84 // 85 // It first computes epsilon closure (states that can be achieved without 86 // consuming characters) for every state that's still matching, 87 // using the same DFS algorithm, but doesn't re-enter states (find a true in 88 // _M_visited), nor follows _S_opcode_match. 89 // 90 // Then apply DFS using every _S_opcode_match (in _M_match_queue) as the start 91 // state. 92 // 93 // It significantly reduces potential duplicate states, so has a better 94 // upper bound; but it requires more overhead. 95 // 96 // Time complexity: \Omega(match_length * match_results.size()) 97 // O(match_length * _M_nfa.size() * match_results.size()) 98 // Space complexity: \Omega(_M_nfa.size() + match_results.size()) 99 // O(_M_nfa.size() * match_results.size()) 100 template<typename _BiIter, typename _Alloc, typename _TraitsT, 101 bool __dfs_mode> 102 template<bool __match_mode> 103 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 104 _M_main() 105 { 106 if (__dfs_mode) 107 { 108 _M_has_sol = false; 109 _M_cur_results = _M_results; 110 _M_dfs<__match_mode>(_M_start_state); 111 return _M_has_sol; 112 } 113 else 114 { 115 _M_match_queue->push_back(make_pair(_M_start_state, _M_results)); 116 bool __ret = false; 117 while (1) 118 { 119 _M_has_sol = false; 120 if (_M_match_queue->empty()) 121 break; 122 _M_visited->assign(_M_visited->size(), false); 123 auto __old_queue = std::move(*_M_match_queue); 124 for (auto& __task : __old_queue) 125 { 126 _M_cur_results = std::move(__task.second); 127 _M_dfs<__match_mode>(__task.first); 128 } 129 if (!__match_mode) 130 __ret |= _M_has_sol; 131 if (_M_current == _M_end) 132 break; 133 ++_M_current; 134 } 135 if (__match_mode) 136 __ret = _M_has_sol; 137 return __ret; 138 } 139 } 140 141 // Return whether now match the given sub-NFA. 142 template<typename _BiIter, typename _Alloc, typename _TraitsT, 143 bool __dfs_mode> 144 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 145 _M_lookahead(_State<_TraitsT> __state) 146 { 147 _ResultsVec __what(_M_cur_results.size()); 148 auto __sub = std::unique_ptr<_Executor>(new _Executor(_M_current, 149 _M_end, 150 __what, 151 _M_re, 152 _M_flags)); 153 __sub->_M_start_state = __state._M_alt; 154 if (__sub->_M_search_from_first()) 155 { 156 for (size_t __i = 0; __i < __what.size(); __i++) 157 if (__what[__i].matched) 158 _M_cur_results[__i] = __what[__i]; 159 return true; 160 } 161 return false; 162 } 163 164 // TODO: Use a function vector to dispatch, instead of using switch-case. 165 template<typename _BiIter, typename _Alloc, typename _TraitsT, 166 bool __dfs_mode> 167 template<bool __match_mode> 168 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 169 _M_dfs(_StateIdT __i) 170 { 171 if (!__dfs_mode) 172 { 173 if ((*_M_visited)[__i]) 174 return; 175 (*_M_visited)[__i] = true; 176 } 177 178 const auto& __state = _M_nfa[__i]; 179 // Every change on _M_cur_results and _M_current will be rolled back after 180 // finishing the recursion step. 181 switch (__state._M_opcode) 182 { 183 // _M_alt branch is "match once more", while _M_next is "get me out 184 // of this quantifier". Executing _M_next first or _M_alt first don't 185 // mean the same thing, and we need to choose the correct order under 186 // given greedy mode. 187 case _S_opcode_alternative: 188 // Greedy. 189 if (!__state._M_neg) 190 { 191 // "Once more" is preferred in greedy mode. 192 _M_dfs<__match_mode>(__state._M_alt); 193 // If it's DFS executor and already accepted, we're done. 194 if (!__dfs_mode || !_M_has_sol) 195 _M_dfs<__match_mode>(__state._M_next); 196 } 197 else // Non-greedy mode 198 { 199 if (__dfs_mode) 200 { 201 // vice-versa. 202 _M_dfs<__match_mode>(__state._M_next); 203 if (!_M_has_sol) 204 _M_dfs<__match_mode>(__state._M_alt); 205 } 206 else 207 { 208 // DON'T attempt anything, because there's already another 209 // state with higher priority accepted. This state cannot be 210 // better by attempting its next node. 211 if (!_M_has_sol) 212 { 213 _M_dfs<__match_mode>(__state._M_next); 214 // DON'T attempt anything if it's already accepted. An 215 // accepted state *must* be better than a solution that 216 // matches a non-greedy quantifier one more time. 217 if (!_M_has_sol) 218 _M_dfs<__match_mode>(__state._M_alt); 219 } 220 } 221 } 222 break; 223 case _S_opcode_subexpr_begin: 224 // If there's nothing changed since last visit, do NOT continue. 225 // This prevents the executor from get into infinite loop when using 226 // "()*" to match "". 227 if (!_M_cur_results[__state._M_subexpr].matched 228 || _M_cur_results[__state._M_subexpr].first != _M_current) 229 { 230 auto& __res = _M_cur_results[__state._M_subexpr]; 231 auto __back = __res.first; 232 __res.first = _M_current; 233 _M_dfs<__match_mode>(__state._M_next); 234 __res.first = __back; 235 } 236 break; 237 case _S_opcode_subexpr_end: 238 if (_M_cur_results[__state._M_subexpr].second != _M_current 239 || _M_cur_results[__state._M_subexpr].matched != true) 240 { 241 auto& __res = _M_cur_results[__state._M_subexpr]; 242 auto __back = __res; 243 __res.second = _M_current; 244 __res.matched = true; 245 _M_dfs<__match_mode>(__state._M_next); 246 __res = __back; 247 } 248 else 249 _M_dfs<__match_mode>(__state._M_next); 250 break; 251 case _S_opcode_line_begin_assertion: 252 if (_M_at_begin()) 253 _M_dfs<__match_mode>(__state._M_next); 254 break; 255 case _S_opcode_line_end_assertion: 256 if (_M_at_end()) 257 _M_dfs<__match_mode>(__state._M_next); 258 break; 259 case _S_opcode_word_boundary: 260 if (_M_word_boundary(__state) == !__state._M_neg) 261 _M_dfs<__match_mode>(__state._M_next); 262 break; 263 // Here __state._M_alt offers a single start node for a sub-NFA. 264 // We recursively invoke our algorithm to match the sub-NFA. 265 case _S_opcode_subexpr_lookahead: 266 if (_M_lookahead(__state) == !__state._M_neg) 267 _M_dfs<__match_mode>(__state._M_next); 268 break; 269 case _S_opcode_match: 270 if (__dfs_mode) 271 { 272 if (_M_current != _M_end && __state._M_matches(*_M_current)) 273 { 274 ++_M_current; 275 _M_dfs<__match_mode>(__state._M_next); 276 --_M_current; 277 } 278 } 279 else 280 if (__state._M_matches(*_M_current)) 281 _M_match_queue->push_back(make_pair(__state._M_next, 282 _M_cur_results)); 283 break; 284 // First fetch the matched result from _M_cur_results as __submatch; 285 // then compare it with 286 // (_M_current, _M_current + (__submatch.second - __submatch.first)). 287 // If matched, keep going; else just return and try another state. 288 case _S_opcode_backref: 289 { 290 _GLIBCXX_DEBUG_ASSERT(__dfs_mode); 291 auto& __submatch = _M_cur_results[__state._M_backref_index]; 292 if (!__submatch.matched) 293 break; 294 auto __last = _M_current; 295 for (auto __tmp = __submatch.first; 296 __last != _M_end && __tmp != __submatch.second; 297 ++__tmp) 298 ++__last; 299 if (_M_re._M_traits.transform(__submatch.first, 300 __submatch.second) 301 == _M_re._M_traits.transform(_M_current, __last)) 302 { 303 if (__last != _M_current) 304 { 305 auto __backup = _M_current; 306 _M_current = __last; 307 _M_dfs<__match_mode>(__state._M_next); 308 _M_current = __backup; 309 } 310 else 311 _M_dfs<__match_mode>(__state._M_next); 312 } 313 } 314 break; 315 case _S_opcode_accept: 316 if (__dfs_mode) 317 { 318 _GLIBCXX_DEBUG_ASSERT(!_M_has_sol); 319 if (__match_mode) 320 _M_has_sol = _M_current == _M_end; 321 else 322 _M_has_sol = true; 323 if (_M_current == _M_begin 324 && (_M_flags & regex_constants::match_not_null)) 325 _M_has_sol = false; 326 if (_M_has_sol) 327 _M_results = _M_cur_results; 328 } 329 else 330 { 331 if (_M_current == _M_begin 332 && (_M_flags & regex_constants::match_not_null)) 333 break; 334 if (!__match_mode || _M_current == _M_end) 335 if (!_M_has_sol) 336 { 337 _M_has_sol = true; 338 _M_results = _M_cur_results; 339 } 340 } 341 break; 342 default: 343 _GLIBCXX_DEBUG_ASSERT(false); 344 } 345 } 346 347 // Return whether now is at some word boundary. 348 template<typename _BiIter, typename _Alloc, typename _TraitsT, 349 bool __dfs_mode> 350 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 351 _M_word_boundary(_State<_TraitsT> __state) const 352 { 353 // By definition. 354 bool __ans = false; 355 auto __pre = _M_current; 356 --__pre; 357 if (!(_M_at_begin() && _M_at_end())) 358 { 359 if (_M_at_begin()) 360 __ans = _M_is_word(*_M_current) 361 && !(_M_flags & regex_constants::match_not_bow); 362 else if (_M_at_end()) 363 __ans = _M_is_word(*__pre) 364 && !(_M_flags & regex_constants::match_not_eow); 365 else 366 __ans = _M_is_word(*_M_current) 367 != _M_is_word(*__pre); 368 } 369 return __ans; 370 } 371 372 _GLIBCXX_END_NAMESPACE_VERSION 373 } // namespace __detail 374 } // namespace 375
