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>:: _M_search()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>:: _M_main_dispatch(_Match_mode __match_mode,__dfs)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>:: _M_main_dispatch(_Match_mode __match_mode,__bfs)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>:: _M_lookahead(_State<_TraitsT> __state)148 _M_lookahead(_State<_TraitsT> __state) 149 { 150 // Backreferences may refer to captured content. 151 // We may want to make this faster by not copying, 152 // but let's not be clever prematurely. 153 _ResultsVec __what(_M_cur_results); 154 _Executor __sub(_M_current, _M_end, __what, _M_re, _M_flags); 155 __sub._M_states._M_start = __state._M_alt; 156 if (__sub._M_search_from_first()) 157 { 158 for (size_t __i = 0; __i < __what.size(); __i++) 159 if (__what[__i].matched) 160 _M_cur_results[__i] = __what[__i]; 161 return true; 162 } 163 return false; 164 } 165 166 // __rep_count records how many times (__rep_count.second) 167 // this node is visited under certain input iterator 168 // (__rep_count.first). This prevent the executor from entering 169 // infinite loop by refusing to continue when it's already been 170 // visited more than twice. It's `twice` instead of `once` because 171 // we need to spare one more time for potential group capture. 172 template<typename _BiIter, typename _Alloc, typename _TraitsT, 173 bool __dfs_mode> 174 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_rep_once_more(_Match_mode __match_mode,_StateIdT __i)175 _M_rep_once_more(_Match_mode __match_mode, _StateIdT __i) 176 { 177 const auto& __state = _M_nfa[__i]; 178 auto& __rep_count = _M_rep_count[__i]; 179 if (__rep_count.second == 0 || __rep_count.first != _M_current) 180 { 181 auto __back = __rep_count; 182 __rep_count.first = _M_current; 183 __rep_count.second = 1; 184 _M_dfs(__match_mode, __state._M_alt); 185 __rep_count = __back; 186 } 187 else 188 { 189 if (__rep_count.second < 2) 190 { 191 __rep_count.second++; 192 _M_dfs(__match_mode, __state._M_alt); 193 __rep_count.second--; 194 } 195 } 196 }; 197 198 template<typename _BiIter, typename _Alloc, typename _TraitsT, 199 bool __dfs_mode> 200 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_dfs(_Match_mode __match_mode,_StateIdT __i)201 _M_dfs(_Match_mode __match_mode, _StateIdT __i) 202 { 203 if (_M_states._M_visited(__i)) 204 return; 205 206 const auto& __state = _M_nfa[__i]; 207 // Every change on _M_cur_results and _M_current will be rolled back after 208 // finishing the recursion step. 209 switch (__state._M_opcode) 210 { 211 // _M_alt branch is "match once more", while _M_next is "get me out 212 // of this quantifier". Executing _M_next first or _M_alt first don't 213 // mean the same thing, and we need to choose the correct order under 214 // given greedy mode. 215 case _S_opcode_repeat: 216 { 217 // Greedy. 218 if (!__state._M_neg) 219 { 220 _M_rep_once_more(__match_mode, __i); 221 // If it's DFS executor and already accepted, we're done. 222 if (!__dfs_mode || !_M_has_sol) 223 _M_dfs(__match_mode, __state._M_next); 224 } 225 else // Non-greedy mode 226 { 227 if (__dfs_mode) 228 { 229 // vice-versa. 230 _M_dfs(__match_mode, __state._M_next); 231 if (!_M_has_sol) 232 _M_rep_once_more(__match_mode, __i); 233 } 234 else 235 { 236 // DON'T attempt anything, because there's already another 237 // state with higher priority accepted. This state cannot 238 // be better by attempting its next node. 239 if (!_M_has_sol) 240 { 241 _M_dfs(__match_mode, __state._M_next); 242 // DON'T attempt anything if it's already accepted. An 243 // accepted state *must* be better than a solution that 244 // matches a non-greedy quantifier one more time. 245 if (!_M_has_sol) 246 _M_rep_once_more(__match_mode, __i); 247 } 248 } 249 } 250 } 251 break; 252 case _S_opcode_subexpr_begin: 253 { 254 auto& __res = _M_cur_results[__state._M_subexpr]; 255 auto __back = __res.first; 256 __res.first = _M_current; 257 _M_dfs(__match_mode, __state._M_next); 258 __res.first = __back; 259 } 260 break; 261 case _S_opcode_subexpr_end: 262 { 263 auto& __res = _M_cur_results[__state._M_subexpr]; 264 auto __back = __res; 265 __res.second = _M_current; 266 __res.matched = true; 267 _M_dfs(__match_mode, __state._M_next); 268 __res = __back; 269 } 270 break; 271 case _S_opcode_line_begin_assertion: 272 if (_M_at_begin()) 273 _M_dfs(__match_mode, __state._M_next); 274 break; 275 case _S_opcode_line_end_assertion: 276 if (_M_at_end()) 277 _M_dfs(__match_mode, __state._M_next); 278 break; 279 case _S_opcode_word_boundary: 280 if (_M_word_boundary() == !__state._M_neg) 281 _M_dfs(__match_mode, __state._M_next); 282 break; 283 // Here __state._M_alt offers a single start node for a sub-NFA. 284 // We recursively invoke our algorithm to match the sub-NFA. 285 case _S_opcode_subexpr_lookahead: 286 if (_M_lookahead(__state) == !__state._M_neg) 287 _M_dfs(__match_mode, __state._M_next); 288 break; 289 case _S_opcode_match: 290 if (_M_current == _M_end) 291 break; 292 if (__dfs_mode) 293 { 294 if (__state._M_matches(*_M_current)) 295 { 296 ++_M_current; 297 _M_dfs(__match_mode, __state._M_next); 298 --_M_current; 299 } 300 } 301 else 302 if (__state._M_matches(*_M_current)) 303 _M_states._M_queue(__state._M_next, _M_cur_results); 304 break; 305 // First fetch the matched result from _M_cur_results as __submatch; 306 // then compare it with 307 // (_M_current, _M_current + (__submatch.second - __submatch.first)). 308 // If matched, keep going; else just return and try another state. 309 case _S_opcode_backref: 310 { 311 _GLIBCXX_DEBUG_ASSERT(__dfs_mode); 312 auto& __submatch = _M_cur_results[__state._M_backref_index]; 313 if (!__submatch.matched) 314 break; 315 auto __last = _M_current; 316 for (auto __tmp = __submatch.first; 317 __last != _M_end && __tmp != __submatch.second; 318 ++__tmp) 319 ++__last; 320 if (_M_re._M_automaton->_M_traits.transform(__submatch.first, 321 __submatch.second) 322 == _M_re._M_automaton->_M_traits.transform(_M_current, __last)) 323 { 324 if (__last != _M_current) 325 { 326 auto __backup = _M_current; 327 _M_current = __last; 328 _M_dfs(__match_mode, __state._M_next); 329 _M_current = __backup; 330 } 331 else 332 _M_dfs(__match_mode, __state._M_next); 333 } 334 } 335 break; 336 case _S_opcode_accept: 337 if (__dfs_mode) 338 { 339 _GLIBCXX_DEBUG_ASSERT(!_M_has_sol); 340 if (__match_mode == _Match_mode::_Exact) 341 _M_has_sol = _M_current == _M_end; 342 else 343 _M_has_sol = true; 344 if (_M_current == _M_begin 345 && (_M_flags & regex_constants::match_not_null)) 346 _M_has_sol = false; 347 if (_M_has_sol) 348 { 349 if (_M_nfa._M_flags & regex_constants::ECMAScript) 350 _M_results = _M_cur_results; 351 else // POSIX 352 { 353 _GLIBCXX_DEBUG_ASSERT(_M_states._M_get_sol_pos()); 354 // Here's POSIX's logic: match the longest one. However 355 // we never know which one (lhs or rhs of "|") is longer 356 // unless we try both of them and compare the results. 357 // The member variable _M_sol_pos records the end 358 // position of the last successful match. It's better 359 // to be larger, because POSIX regex is always greedy. 360 // TODO: This could be slow. 361 if (*_M_states._M_get_sol_pos() == _BiIter() 362 || std::distance(_M_begin, 363 *_M_states._M_get_sol_pos()) 364 < std::distance(_M_begin, _M_current)) 365 { 366 *_M_states._M_get_sol_pos() = _M_current; 367 _M_results = _M_cur_results; 368 } 369 } 370 } 371 } 372 else 373 { 374 if (_M_current == _M_begin 375 && (_M_flags & regex_constants::match_not_null)) 376 break; 377 if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end) 378 if (!_M_has_sol) 379 { 380 _M_has_sol = true; 381 _M_results = _M_cur_results; 382 } 383 } 384 break; 385 case _S_opcode_alternative: 386 if (_M_nfa._M_flags & regex_constants::ECMAScript) 387 { 388 // TODO: Let BFS support ECMAScript's alternative operation. 389 _GLIBCXX_DEBUG_ASSERT(__dfs_mode); 390 _M_dfs(__match_mode, __state._M_alt); 391 // Pick lhs if it matches. Only try rhs if it doesn't. 392 if (!_M_has_sol) 393 _M_dfs(__match_mode, __state._M_next); 394 } 395 else 396 { 397 // Try both and compare the result. 398 // See "case _S_opcode_accept:" handling above. 399 _M_dfs(__match_mode, __state._M_alt); 400 auto __has_sol = _M_has_sol; 401 _M_has_sol = false; 402 _M_dfs(__match_mode, __state._M_next); 403 _M_has_sol |= __has_sol; 404 } 405 break; 406 default: 407 _GLIBCXX_DEBUG_ASSERT(false); 408 } 409 } 410 411 // Return whether now is at some word boundary. 412 template<typename _BiIter, typename _Alloc, typename _TraitsT, 413 bool __dfs_mode> 414 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_word_boundary() const415 _M_word_boundary() const 416 { 417 bool __left_is_word = false; 418 if (_M_current != _M_begin 419 || (_M_flags & regex_constants::match_prev_avail)) 420 { 421 auto __prev = _M_current; 422 if (_M_is_word(*std::prev(__prev))) 423 __left_is_word = true; 424 } 425 bool __right_is_word = 426 _M_current != _M_end && _M_is_word(*_M_current); 427 428 if (__left_is_word == __right_is_word) 429 return false; 430 if (__left_is_word && !(_M_flags & regex_constants::match_not_eow)) 431 return true; 432 if (__right_is_word && !(_M_flags & regex_constants::match_not_bow)) 433 return true; 434 return false; 435 } 436 437 _GLIBCXX_END_NAMESPACE_VERSION 438 } // namespace __detail 439 } // namespace 440