1 // class template regex -*- C++ -*- 2 3 // Copyright (C) 2013-2015 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_search_from_first()) 43 return true; 44 if (_M_flags & regex_constants::match_continuous) 45 return false; 46 _M_flags |= regex_constants::match_prev_avail; 47 while (_M_begin != _M_end) 48 { 49 ++_M_begin; 50 if (_M_search_from_first()) 51 return true; 52 } 53 return false; 54 } 55 56 // The _M_main function operates in different modes, DFS mode or BFS mode, 57 // indicated by template parameter __dfs_mode, and dispatches to one of the 58 // _M_main_dispatch overloads. 59 // 60 // ------------------------------------------------------------ 61 // 62 // DFS mode: 63 // 64 // It applies a Depth-First-Search (aka backtracking) on given NFA and input 65 // string. 66 // At the very beginning the executor stands in the start state, then it 67 // tries every possible state transition in current state recursively. Some 68 // state transitions consume input string, say, a single-char-matcher or a 69 // back-reference matcher; some don't, like assertion or other anchor nodes. 70 // When the input is exhausted and/or the current state is an accepting 71 // state, the whole executor returns true. 72 // 73 // TODO: This approach is exponentially slow for certain input. 74 // Try to compile the NFA to a DFA. 75 // 76 // Time complexity: \Omega(match_length), O(2^(_M_nfa.size())) 77 // Space complexity: \theta(match_results.size() + match_length) 78 // 79 template<typename _BiIter, typename _Alloc, typename _TraitsT, 80 bool __dfs_mode> 81 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 82 _M_main_dispatch(_Match_mode __match_mode, __dfs) 83 { 84 _M_has_sol = false; 85 *_M_states._M_get_sol_pos() = _BiIter(); 86 _M_cur_results = _M_results; 87 _M_dfs(__match_mode, _M_states._M_start); 88 return _M_has_sol; 89 } 90 91 // ------------------------------------------------------------ 92 // 93 // BFS mode: 94 // 95 // Russ Cox's article (http://swtch.com/~rsc/regexp/regexp1.html) 96 // explained this algorithm clearly. 97 // 98 // It first computes epsilon closure (states that can be achieved without 99 // consuming characters) for every state that's still matching, 100 // using the same DFS algorithm, but doesn't re-enter states (using 101 // _M_states._M_visited to check), nor follow _S_opcode_match. 102 // 103 // Then apply DFS using every _S_opcode_match (in _M_states._M_match_queue) 104 // as the start state. 105 // 106 // It significantly reduces potential duplicate states, so has a better 107 // upper bound; but it requires more overhead. 108 // 109 // Time complexity: \Omega(match_length * match_results.size()) 110 // O(match_length * _M_nfa.size() * match_results.size()) 111 // Space complexity: \Omega(_M_nfa.size() + match_results.size()) 112 // O(_M_nfa.size() * match_results.size()) 113 template<typename _BiIter, typename _Alloc, typename _TraitsT, 114 bool __dfs_mode> 115 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 116 _M_main_dispatch(_Match_mode __match_mode, __bfs) 117 { 118 _M_states._M_queue(_M_states._M_start, _M_results); 119 bool __ret = false; 120 while (1) 121 { 122 _M_has_sol = false; 123 if (_M_states._M_match_queue.empty()) 124 break; 125 std::fill_n(_M_states._M_visited_states.get(), _M_nfa.size(), false); 126 auto __old_queue = std::move(_M_states._M_match_queue); 127 for (auto& __task : __old_queue) 128 { 129 _M_cur_results = std::move(__task.second); 130 _M_dfs(__match_mode, __task.first); 131 } 132 if (__match_mode == _Match_mode::_Prefix) 133 __ret |= _M_has_sol; 134 if (_M_current == _M_end) 135 break; 136 ++_M_current; 137 } 138 if (__match_mode == _Match_mode::_Exact) 139 __ret = _M_has_sol; 140 _M_states._M_match_queue.clear(); 141 return __ret; 142 } 143 144 // Return whether now match the given sub-NFA. 145 template<typename _BiIter, typename _Alloc, typename _TraitsT, 146 bool __dfs_mode> 147 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 148 _M_lookahead(_State<_TraitsT> __state) 149 { 150 _ResultsVec __what(_M_cur_results.size()); 151 _Executor __sub(_M_current, _M_end, __what, _M_re, _M_flags); 152 __sub._M_states._M_start = __state._M_alt; 153 if (__sub._M_search_from_first()) 154 { 155 for (size_t __i = 0; __i < __what.size(); __i++) 156 if (__what[__i].matched) 157 _M_cur_results[__i] = __what[__i]; 158 return true; 159 } 160 return false; 161 } 162 163 // __rep_count records how many times (__rep_count.second) 164 // this node is visited under certain input iterator 165 // (__rep_count.first). This prevent the executor from entering 166 // infinite loop by refusing to continue when it's already been 167 // visited more than twice. It's `twice` instead of `once` because 168 // we need to spare one more time for potential group capture. 169 template<typename _BiIter, typename _Alloc, typename _TraitsT, 170 bool __dfs_mode> 171 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 172 _M_rep_once_more(_Match_mode __match_mode, _StateIdT __i) 173 { 174 const auto& __state = _M_nfa[__i]; 175 auto& __rep_count = _M_rep_count[__i]; 176 if (__rep_count.second == 0 || __rep_count.first != _M_current) 177 { 178 auto __back = __rep_count; 179 __rep_count.first = _M_current; 180 __rep_count.second = 1; 181 _M_dfs(__match_mode, __state._M_alt); 182 __rep_count = __back; 183 } 184 else 185 { 186 if (__rep_count.second < 2) 187 { 188 __rep_count.second++; 189 _M_dfs(__match_mode, __state._M_alt); 190 __rep_count.second--; 191 } 192 } 193 }; 194 195 template<typename _BiIter, typename _Alloc, typename _TraitsT, 196 bool __dfs_mode> 197 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 198 _M_dfs(_Match_mode __match_mode, _StateIdT __i) 199 { 200 if (_M_states._M_visited(__i)) 201 return; 202 203 const auto& __state = _M_nfa[__i]; 204 // Every change on _M_cur_results and _M_current will be rolled back after 205 // finishing the recursion step. 206 switch (__state._M_opcode) 207 { 208 // _M_alt branch is "match once more", while _M_next is "get me out 209 // of this quantifier". Executing _M_next first or _M_alt first don't 210 // mean the same thing, and we need to choose the correct order under 211 // given greedy mode. 212 case _S_opcode_repeat: 213 { 214 // Greedy. 215 if (!__state._M_neg) 216 { 217 _M_rep_once_more(__match_mode, __i); 218 // If it's DFS executor and already accepted, we're done. 219 if (!__dfs_mode || !_M_has_sol) 220 _M_dfs(__match_mode, __state._M_next); 221 } 222 else // Non-greedy mode 223 { 224 if (__dfs_mode) 225 { 226 // vice-versa. 227 _M_dfs(__match_mode, __state._M_next); 228 if (!_M_has_sol) 229 _M_rep_once_more(__match_mode, __i); 230 } 231 else 232 { 233 // DON'T attempt anything, because there's already another 234 // state with higher priority accepted. This state cannot 235 // be better by attempting its next node. 236 if (!_M_has_sol) 237 { 238 _M_dfs(__match_mode, __state._M_next); 239 // DON'T attempt anything if it's already accepted. An 240 // accepted state *must* be better than a solution that 241 // matches a non-greedy quantifier one more time. 242 if (!_M_has_sol) 243 _M_rep_once_more(__match_mode, __i); 244 } 245 } 246 } 247 } 248 break; 249 case _S_opcode_subexpr_begin: 250 { 251 auto& __res = _M_cur_results[__state._M_subexpr]; 252 auto __back = __res.first; 253 __res.first = _M_current; 254 _M_dfs(__match_mode, __state._M_next); 255 __res.first = __back; 256 } 257 break; 258 case _S_opcode_subexpr_end: 259 { 260 auto& __res = _M_cur_results[__state._M_subexpr]; 261 auto __back = __res; 262 __res.second = _M_current; 263 __res.matched = true; 264 _M_dfs(__match_mode, __state._M_next); 265 __res = __back; 266 } 267 break; 268 case _S_opcode_line_begin_assertion: 269 if (_M_at_begin()) 270 _M_dfs(__match_mode, __state._M_next); 271 break; 272 case _S_opcode_line_end_assertion: 273 if (_M_at_end()) 274 _M_dfs(__match_mode, __state._M_next); 275 break; 276 case _S_opcode_word_boundary: 277 if (_M_word_boundary() == !__state._M_neg) 278 _M_dfs(__match_mode, __state._M_next); 279 break; 280 // Here __state._M_alt offers a single start node for a sub-NFA. 281 // We recursively invoke our algorithm to match the sub-NFA. 282 case _S_opcode_subexpr_lookahead: 283 if (_M_lookahead(__state) == !__state._M_neg) 284 _M_dfs(__match_mode, __state._M_next); 285 break; 286 case _S_opcode_match: 287 if (_M_current == _M_end) 288 break; 289 if (__dfs_mode) 290 { 291 if (__state._M_matches(*_M_current)) 292 { 293 ++_M_current; 294 _M_dfs(__match_mode, __state._M_next); 295 --_M_current; 296 } 297 } 298 else 299 if (__state._M_matches(*_M_current)) 300 _M_states._M_queue(__state._M_next, _M_cur_results); 301 break; 302 // First fetch the matched result from _M_cur_results as __submatch; 303 // then compare it with 304 // (_M_current, _M_current + (__submatch.second - __submatch.first)). 305 // If matched, keep going; else just return and try another state. 306 case _S_opcode_backref: 307 { 308 _GLIBCXX_DEBUG_ASSERT(__dfs_mode); 309 auto& __submatch = _M_cur_results[__state._M_backref_index]; 310 if (!__submatch.matched) 311 break; 312 auto __last = _M_current; 313 for (auto __tmp = __submatch.first; 314 __last != _M_end && __tmp != __submatch.second; 315 ++__tmp) 316 ++__last; 317 if (_M_re._M_automaton->_M_traits.transform(__submatch.first, 318 __submatch.second) 319 == _M_re._M_automaton->_M_traits.transform(_M_current, __last)) 320 { 321 if (__last != _M_current) 322 { 323 auto __backup = _M_current; 324 _M_current = __last; 325 _M_dfs(__match_mode, __state._M_next); 326 _M_current = __backup; 327 } 328 else 329 _M_dfs(__match_mode, __state._M_next); 330 } 331 } 332 break; 333 case _S_opcode_accept: 334 if (__dfs_mode) 335 { 336 _GLIBCXX_DEBUG_ASSERT(!_M_has_sol); 337 if (__match_mode == _Match_mode::_Exact) 338 _M_has_sol = _M_current == _M_end; 339 else 340 _M_has_sol = true; 341 if (_M_current == _M_begin 342 && (_M_flags & regex_constants::match_not_null)) 343 _M_has_sol = false; 344 if (_M_has_sol) 345 { 346 if (_M_nfa._M_flags & regex_constants::ECMAScript) 347 _M_results = _M_cur_results; 348 else // POSIX 349 { 350 _GLIBCXX_DEBUG_ASSERT(_M_states._M_get_sol_pos()); 351 // Here's POSIX's logic: match the longest one. However 352 // we never know which one (lhs or rhs of "|") is longer 353 // unless we try both of them and compare the results. 354 // The member variable _M_sol_pos records the end 355 // position of the last successful match. It's better 356 // to be larger, because POSIX regex is always greedy. 357 // TODO: This could be slow. 358 if (*_M_states._M_get_sol_pos() == _BiIter() 359 || std::distance(_M_begin, 360 *_M_states._M_get_sol_pos()) 361 < std::distance(_M_begin, _M_current)) 362 { 363 *_M_states._M_get_sol_pos() = _M_current; 364 _M_results = _M_cur_results; 365 } 366 } 367 } 368 } 369 else 370 { 371 if (_M_current == _M_begin 372 && (_M_flags & regex_constants::match_not_null)) 373 break; 374 if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end) 375 if (!_M_has_sol) 376 { 377 _M_has_sol = true; 378 _M_results = _M_cur_results; 379 } 380 } 381 break; 382 case _S_opcode_alternative: 383 if (_M_nfa._M_flags & regex_constants::ECMAScript) 384 { 385 // TODO: Let BFS support ECMAScript's alternative operation. 386 _GLIBCXX_DEBUG_ASSERT(__dfs_mode); 387 _M_dfs(__match_mode, __state._M_alt); 388 // Pick lhs if it matches. Only try rhs if it doesn't. 389 if (!_M_has_sol) 390 _M_dfs(__match_mode, __state._M_next); 391 } 392 else 393 { 394 // Try both and compare the result. 395 // See "case _S_opcode_accept:" handling above. 396 _M_dfs(__match_mode, __state._M_alt); 397 auto __has_sol = _M_has_sol; 398 _M_has_sol = false; 399 _M_dfs(__match_mode, __state._M_next); 400 _M_has_sol |= __has_sol; 401 } 402 break; 403 default: 404 _GLIBCXX_DEBUG_ASSERT(false); 405 } 406 } 407 408 // Return whether now is at some word boundary. 409 template<typename _BiIter, typename _Alloc, typename _TraitsT, 410 bool __dfs_mode> 411 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 412 _M_word_boundary() const 413 { 414 bool __left_is_word = false; 415 if (_M_current != _M_begin 416 || (_M_flags & regex_constants::match_prev_avail)) 417 { 418 auto __prev = _M_current; 419 if (_M_is_word(*std::prev(__prev))) 420 __left_is_word = true; 421 } 422 bool __right_is_word = 423 _M_current != _M_end && _M_is_word(*_M_current); 424 425 if (__left_is_word == __right_is_word) 426 return false; 427 if (__left_is_word && !(_M_flags & regex_constants::match_not_eow)) 428 return true; 429 if (__right_is_word && !(_M_flags & regex_constants::match_not_bow)) 430 return true; 431 return false; 432 } 433 434 _GLIBCXX_END_NAMESPACE_VERSION 435 } // namespace __detail 436 } // namespace 437