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1 // class template regex -*- C++ -*- 2 3 // Copyright (C) 2013-2025 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 _GLIBCXX_BEGIN_NAMESPACE_VERSION 34 35 #pragma GCC diagnostic push 36 #pragma GCC diagnostic ignored "-Wc++17-extensions" // if constexpr 37 namespace __detail 38 { 39 template<typename _BiIter, typename _Alloc, typename _TraitsT, 40 bool __dfs_mode> 41 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 42 _M_search() 43 { 44 if (_M_search_from_first()) 45 return true; 46 if (_M_flags & regex_constants::match_continuous) 47 return false; 48 _M_flags |= regex_constants::match_prev_avail; 49 while (_M_begin != _M_end) 50 { 51 ++_M_begin; 52 if (_M_search_from_first()) 53 return true; 54 } 55 return false; 56 } 57 58 // The _M_main function operates in different modes, DFS mode or BFS mode, 59 // indicated by template parameter __dfs_mode, and dispatches to one of the 60 // _M_main_dispatch overloads. 61 // 62 // ------------------------------------------------------------ 63 // 64 // DFS mode: 65 // 66 // It applies a Depth-First-Search (aka backtracking) on given NFA and input 67 // string. 68 // At the very beginning the executor stands in the start state, then it 69 // tries every possible state transition in current state recursively. Some 70 // state transitions consume input string, say, a single-char-matcher or a 71 // back-reference matcher; some don't, like assertion or other anchor nodes. 72 // When the input is exhausted and/or the current state is an accepting 73 // state, the whole executor returns true. 74 // 75 // TODO: This approach is exponentially slow for certain input. 76 // Try to compile the NFA to a DFA. 77 // 78 // Time complexity: \Omega(match_length), O(2^(_M_nfa.size())) 79 // Space complexity: \theta(match_results.size() + match_length) 80 // 81 template<typename _BiIter, typename _Alloc, typename _TraitsT, 82 bool __dfs_mode> 83 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 84 _M_main_dispatch(_Match_mode __match_mode, __dfs) 85 { 86 _M_has_sol = false; 87 *_M_states._M_get_sol_pos() = _BiIter(); 88 _M_cur_results = _M_results; 89 _M_dfs(__match_mode, _M_states._M_start); 90 return _M_has_sol; 91 } 92 93 // ------------------------------------------------------------ 94 // 95 // BFS mode: 96 // 97 // Russ Cox's article (http://swtch.com/~rsc/regexp/regexp1.html) 98 // explained this algorithm clearly. 99 // 100 // It first computes epsilon closure (states that can be achieved without 101 // consuming characters) for every state that's still matching, 102 // using the same DFS algorithm, but doesn't re-enter states (using 103 // _M_states._M_visited to check), nor follow _S_opcode_match. 104 // 105 // Then apply DFS using every _S_opcode_match (in _M_states._M_match_queue) 106 // as the start state. 107 // 108 // It significantly reduces potential duplicate states, so has a better 109 // upper bound; but it requires more overhead. 110 // 111 // Time complexity: \Omega(match_length * match_results.size()) 112 // O(match_length * _M_nfa.size() * match_results.size()) 113 // Space complexity: \Omega(_M_nfa.size() + match_results.size()) 114 // O(_M_nfa.size() * match_results.size()) 115 template<typename _BiIter, typename _Alloc, typename _TraitsT, 116 bool __dfs_mode> 117 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 118 _M_main_dispatch(_Match_mode __match_mode, __bfs) 119 { 120 _M_states._M_queue(_M_states._M_start, _M_results); 121 bool __ret = false; 122 while (1) 123 { 124 _M_has_sol = false; 125 if (_M_states._M_match_queue.empty()) 126 break; 127 std::fill_n(_M_states._M_visited_states, _M_nfa.size(), false); 128 auto __old_queue = std::move(_M_states._M_match_queue); 129 auto __alloc = _M_cur_results.get_allocator(); 130 for (auto& __task : __old_queue) 131 { 132 _M_cur_results = _ResultsVec(std::move(__task.second), __alloc); 133 _M_dfs(__match_mode, __task.first); 134 } 135 if (__match_mode == _Match_mode::_Prefix) 136 __ret |= _M_has_sol; 137 if (_M_current == _M_end) 138 break; 139 ++_M_current; 140 } 141 if (__match_mode == _Match_mode::_Exact) 142 __ret = _M_has_sol; 143 _M_states._M_match_queue.clear(); 144 return __ret; 145 } 146 147 // Return whether now match the given sub-NFA. 148 template<typename _BiIter, typename _Alloc, typename _TraitsT, 149 bool __dfs_mode> 150 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 151 _M_lookahead(_StateIdT __next) 152 { 153 // Backreferences may refer to captured content. 154 // We may want to make this faster by not copying, 155 // but let's not be clever prematurely. 156 _ResultsVec __what(_M_cur_results); 157 _Executor __sub(_M_current, _M_end, __what, _M_re, _M_flags); 158 __sub._M_states._M_start = __next; 159 if (__sub._M_search_from_first()) 160 { 161 for (size_t __i = 0; __i < __what.size(); __i++) 162 if (__what[__i].matched) 163 _M_cur_results[__i] = __what[__i]; 164 return true; 165 } 166 return false; 167 } 168 169 // __rep_count records how many times (__rep_count.second) 170 // this node is visited under certain input iterator 171 // (__rep_count.first). This prevent the executor from entering 172 // infinite loop by refusing to continue when it's already been 173 // visited more than twice. It's `twice` instead of `once` because 174 // we need to spare one more time for potential group capture. 175 template<typename _BiIter, typename _Alloc, typename _TraitsT, 176 bool __dfs_mode> 177 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 178 _M_rep_once_more(_Match_mode __match_mode, _StateIdT __i) 179 { 180 const auto& __state = _M_nfa[__i]; 181 auto& __rep_count = _M_rep_count[__i]; 182 if (__rep_count.second == 0 || __rep_count.first != _M_current) 183 { 184 auto __back = __rep_count; 185 __rep_count.first = _M_current; 186 __rep_count.second = 1; 187 _M_dfs(__match_mode, __state._M_alt); 188 __rep_count = __back; 189 } 190 else 191 { 192 if (__rep_count.second < 2) 193 { 194 __rep_count.second++; 195 _M_dfs(__match_mode, __state._M_alt); 196 __rep_count.second--; 197 } 198 } 199 } 200 201 // _M_alt branch is "match once more", while _M_next is "get me out 202 // of this quantifier". Executing _M_next first or _M_alt first don't 203 // mean the same thing, and we need to choose the correct order under 204 // given greedy mode. 205 template<typename _BiIter, typename _Alloc, typename _TraitsT, 206 bool __dfs_mode> 207 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 208 _M_handle_repeat(_Match_mode __match_mode, _StateIdT __i) 209 { 210 const auto& __state = _M_nfa[__i]; 211 212 // Greedy. 213 if (!__state._M_neg) 214 { 215 _M_rep_once_more(__match_mode, __i); 216 // If it's DFS executor and already accepted, we're done. 217 if (!__dfs_mode || !_M_has_sol) 218 _M_dfs(__match_mode, __state._M_next); 219 } 220 else // Non-greedy mode 221 { 222 if constexpr (__dfs_mode) 223 { 224 // vice-versa. 225 _M_dfs(__match_mode, __state._M_next); 226 if (!_M_has_sol) 227 _M_rep_once_more(__match_mode, __i); 228 } 229 else 230 { 231 // DON'T attempt anything, because there's already another 232 // state with higher priority accepted. This state cannot 233 // be better by attempting its next node. 234 if (!_M_has_sol) 235 { 236 _M_dfs(__match_mode, __state._M_next); 237 // DON'T attempt anything if it's already accepted. An 238 // accepted state *must* be better than a solution that 239 // matches a non-greedy quantifier one more time. 240 if (!_M_has_sol) 241 _M_rep_once_more(__match_mode, __i); 242 } 243 } 244 } 245 } 246 247 template<typename _BiIter, typename _Alloc, typename _TraitsT, 248 bool __dfs_mode> 249 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 250 _M_handle_subexpr_begin(_Match_mode __match_mode, _StateIdT __i) 251 { 252 const auto& __state = _M_nfa[__i]; 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 } 260 261 template<typename _BiIter, typename _Alloc, typename _TraitsT, 262 bool __dfs_mode> 263 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 264 _M_handle_subexpr_end(_Match_mode __match_mode, _StateIdT __i) 265 { 266 const auto& __state = _M_nfa[__i]; 267 268 auto& __res = _M_cur_results[__state._M_subexpr]; 269 auto __back = __res; 270 __res.second = _M_current; 271 __res.matched = true; 272 _M_dfs(__match_mode, __state._M_next); 273 __res = __back; 274 } 275 276 template<typename _BiIter, typename _Alloc, typename _TraitsT, 277 bool __dfs_mode> 278 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 279 _M_handle_line_begin_assertion(_Match_mode __match_mode, _StateIdT __i) 280 { 281 const auto& __state = _M_nfa[__i]; 282 if (_M_at_begin()) 283 _M_dfs(__match_mode, __state._M_next); 284 } 285 286 template<typename _BiIter, typename _Alloc, typename _TraitsT, 287 bool __dfs_mode> 288 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 289 _M_handle_line_end_assertion(_Match_mode __match_mode, _StateIdT __i) 290 { 291 const auto& __state = _M_nfa[__i]; 292 if (_M_at_end()) 293 _M_dfs(__match_mode, __state._M_next); 294 } 295 296 template<typename _BiIter, typename _Alloc, typename _TraitsT, 297 bool __dfs_mode> 298 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 299 _M_handle_word_boundary(_Match_mode __match_mode, _StateIdT __i) 300 { 301 const auto& __state = _M_nfa[__i]; 302 if (_M_word_boundary() == !__state._M_neg) 303 _M_dfs(__match_mode, __state._M_next); 304 } 305 306 // Here __state._M_alt offers a single start node for a sub-NFA. 307 // We recursively invoke our algorithm to match the sub-NFA. 308 template<typename _BiIter, typename _Alloc, typename _TraitsT, 309 bool __dfs_mode> 310 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 311 _M_handle_subexpr_lookahead(_Match_mode __match_mode, _StateIdT __i) 312 { 313 const auto& __state = _M_nfa[__i]; 314 if (_M_lookahead(__state._M_alt) == !__state._M_neg) 315 _M_dfs(__match_mode, __state._M_next); 316 } 317 318 template<typename _BiIter, typename _Alloc, typename _TraitsT, 319 bool __dfs_mode> 320 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 321 _M_handle_match(_Match_mode __match_mode, _StateIdT __i) 322 { 323 const auto& __state = _M_nfa[__i]; 324 325 if (_M_current == _M_end) 326 return; 327 if constexpr (__dfs_mode) 328 { 329 if (__state._M_matches(*_M_current)) 330 { 331 ++_M_current; 332 _M_dfs(__match_mode, __state._M_next); 333 --_M_current; 334 } 335 } 336 else 337 if (__state._M_matches(*_M_current)) 338 _M_states._M_queue(__state._M_next, _M_cur_results); 339 } 340 341 template<typename _BiIter, typename _TraitsT> 342 struct _Backref_matcher 343 { 344 _Backref_matcher(bool /* __icase */, const _TraitsT& __traits) 345 : _M_traits(__traits) { } 346 347 bool 348 _M_apply(_BiIter __expected_begin, 349 _BiIter __expected_end, _BiIter __actual_begin, 350 _BiIter __actual_end) 351 { 352 return _M_traits.transform(__expected_begin, __expected_end) 353 == _M_traits.transform(__actual_begin, __actual_end); 354 } 355 356 const _TraitsT& _M_traits; 357 }; 358 359 template<typename _BiIter, typename _CharT> 360 struct _Backref_matcher<_BiIter, std::regex_traits<_CharT>> 361 { 362 using _TraitsT = std::regex_traits<_CharT>; 363 _Backref_matcher(bool __icase, const _TraitsT& __traits) 364 : _M_icase(__icase), _M_traits(__traits) { } 365 366 bool 367 _M_apply(_BiIter __expected_begin, 368 _BiIter __expected_end, _BiIter __actual_begin, 369 _BiIter __actual_end) 370 { 371 if (!_M_icase) 372 return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end, 373 __actual_begin, __actual_end); 374 typedef std::ctype<_CharT> __ctype_type; 375 const auto& __fctyp = use_facet<__ctype_type>(_M_traits.getloc()); 376 return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end, 377 __actual_begin, __actual_end, 378 [this, &__fctyp](_CharT __lhs, _CharT __rhs) 379 { 380 return __fctyp.tolower(__lhs) 381 == __fctyp.tolower(__rhs); 382 }); 383 } 384 385 bool _M_icase; 386 const _TraitsT& _M_traits; 387 }; 388 389 // First fetch the matched result from _M_cur_results as __submatch; 390 // then compare it with 391 // (_M_current, _M_current + (__submatch.second - __submatch.first)). 392 // If matched, keep going; else just return and try another state. 393 template<typename _BiIter, typename _Alloc, typename _TraitsT, 394 bool __dfs_mode> 395 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 396 _M_handle_backref(_Match_mode __match_mode, _StateIdT __i) 397 { 398 static_assert(__dfs_mode, "this should never be instantiated"); 399 400 const auto& __state = _M_nfa[__i]; 401 auto& __submatch = _M_cur_results[__state._M_backref_index]; 402 if (!__submatch.matched) 403 return; 404 auto __last = _M_current; 405 for (auto __tmp = __submatch.first; 406 __last != _M_end && __tmp != __submatch.second; 407 ++__tmp) 408 ++__last; 409 if (_Backref_matcher<_BiIter, _TraitsT>( 410 _M_re.flags() & regex_constants::icase, 411 _M_re._M_automaton->_M_traits)._M_apply( 412 __submatch.first, __submatch.second, _M_current, __last)) 413 { 414 if (__last != _M_current) 415 { 416 auto __backup = _M_current; 417 _M_current = __last; 418 _M_dfs(__match_mode, __state._M_next); 419 _M_current = __backup; 420 } 421 else 422 _M_dfs(__match_mode, __state._M_next); 423 } 424 } 425 426 template<typename _BiIter, typename _Alloc, typename _TraitsT, 427 bool __dfs_mode> 428 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 429 _M_handle_accept(_Match_mode __match_mode, _StateIdT) 430 { 431 if constexpr (__dfs_mode) 432 { 433 __glibcxx_assert(!_M_has_sol); 434 if (__match_mode == _Match_mode::_Exact) 435 _M_has_sol = _M_current == _M_end; 436 else 437 _M_has_sol = true; 438 if (_M_current == _M_begin 439 && (_M_flags & regex_constants::match_not_null)) 440 _M_has_sol = false; 441 if (_M_has_sol) 442 { 443 if (_M_nfa._M_flags & regex_constants::ECMAScript) 444 _M_results = _M_cur_results; 445 else // POSIX 446 { 447 __glibcxx_assert(_M_states._M_get_sol_pos()); 448 // Here's POSIX's logic: match the longest one. However 449 // we never know which one (lhs or rhs of "|") is longer 450 // unless we try both of them and compare the results. 451 // The member variable _M_sol_pos records the end 452 // position of the last successful match. It's better 453 // to be larger, because POSIX regex is always greedy. 454 // TODO: This could be slow. 455 if (*_M_states._M_get_sol_pos() == _BiIter() 456 || std::distance(_M_begin, 457 *_M_states._M_get_sol_pos()) 458 < std::distance(_M_begin, _M_current)) 459 { 460 *_M_states._M_get_sol_pos() = _M_current; 461 _M_results = _M_cur_results; 462 } 463 } 464 } 465 } 466 else 467 { 468 if (_M_current == _M_begin 469 && (_M_flags & regex_constants::match_not_null)) 470 return; 471 if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end) 472 if (!_M_has_sol) 473 { 474 _M_has_sol = true; 475 _M_results = _M_cur_results; 476 } 477 } 478 } 479 480 template<typename _BiIter, typename _Alloc, typename _TraitsT, 481 bool __dfs_mode> 482 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 483 _M_handle_alternative(_Match_mode __match_mode, _StateIdT __i) 484 { 485 const auto& __state = _M_nfa[__i]; 486 487 if (_M_nfa._M_flags & regex_constants::ECMAScript) 488 { 489 // TODO: Fix BFS support. It is wrong. 490 _M_dfs(__match_mode, __state._M_alt); 491 // Pick lhs if it matches. Only try rhs if it doesn't. 492 if (!_M_has_sol) 493 _M_dfs(__match_mode, __state._M_next); 494 } 495 else 496 { 497 // Try both and compare the result. 498 // See "case _S_opcode_accept:" handling above. 499 _M_dfs(__match_mode, __state._M_alt); 500 auto __has_sol = _M_has_sol; 501 _M_has_sol = false; 502 _M_dfs(__match_mode, __state._M_next); 503 _M_has_sol |= __has_sol; 504 } 505 } 506 507 template<typename _BiIter, typename _Alloc, typename _TraitsT, 508 bool __dfs_mode> 509 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 510 _M_dfs(_Match_mode __match_mode, _StateIdT __i) 511 { 512 if (_M_states._M_visited(__i)) 513 return; 514 515 switch (_M_nfa[__i]._M_opcode()) 516 { 517 case _S_opcode_repeat: 518 _M_handle_repeat(__match_mode, __i); break; 519 case _S_opcode_subexpr_begin: 520 _M_handle_subexpr_begin(__match_mode, __i); break; 521 case _S_opcode_subexpr_end: 522 _M_handle_subexpr_end(__match_mode, __i); break; 523 case _S_opcode_line_begin_assertion: 524 _M_handle_line_begin_assertion(__match_mode, __i); break; 525 case _S_opcode_line_end_assertion: 526 _M_handle_line_end_assertion(__match_mode, __i); break; 527 case _S_opcode_word_boundary: 528 _M_handle_word_boundary(__match_mode, __i); break; 529 case _S_opcode_subexpr_lookahead: 530 _M_handle_subexpr_lookahead(__match_mode, __i); break; 531 case _S_opcode_match: 532 _M_handle_match(__match_mode, __i); break; 533 case _S_opcode_backref: 534 if constexpr (__dfs_mode) 535 _M_handle_backref(__match_mode, __i); 536 else 537 __builtin_unreachable(); 538 break; 539 case _S_opcode_accept: 540 _M_handle_accept(__match_mode, __i); break; 541 case _S_opcode_alternative: 542 _M_handle_alternative(__match_mode, __i); break; 543 default: 544 __glibcxx_assert(false); 545 } 546 } 547 548 // Return whether now is at some word boundary. 549 template<typename _BiIter, typename _Alloc, typename _TraitsT, 550 bool __dfs_mode> 551 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 552 _M_word_boundary() const 553 { 554 if (_M_current == _M_begin && (_M_flags & regex_constants::match_not_bow)) 555 return false; 556 if (_M_current == _M_end && (_M_flags & regex_constants::match_not_eow)) 557 return false; 558 559 bool __left_is_word = false; 560 if (_M_current != _M_begin 561 || (_M_flags & regex_constants::match_prev_avail)) 562 { 563 auto __prev = _M_current; 564 if (_M_is_word(*std::prev(__prev))) 565 __left_is_word = true; 566 } 567 bool __right_is_word = 568 _M_current != _M_end && _M_is_word(*_M_current); 569 570 return __left_is_word != __right_is_word; 571 } 572 } // namespace __detail 573 #pragma GCC diagnostic pop 574 575 _GLIBCXX_END_NAMESPACE_VERSION 576 } // namespace
