1 // class template regex -*- C++ -*- 2 3 // Copyright (C) 2013-2022 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 namespace __detail 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, _M_nfa.size(), false); 126 auto __old_queue = std::move(_M_states._M_match_queue); 127 auto __alloc = _M_cur_results.get_allocator(); 128 for (auto& __task : __old_queue) 129 { 130 _M_cur_results = _ResultsVec(std::move(__task.second), __alloc); 131 _M_dfs(__match_mode, __task.first); 132 } 133 if (__match_mode == _Match_mode::_Prefix) 134 __ret |= _M_has_sol; 135 if (_M_current == _M_end) 136 break; 137 ++_M_current; 138 } 139 if (__match_mode == _Match_mode::_Exact) 140 __ret = _M_has_sol; 141 _M_states._M_match_queue.clear(); 142 return __ret; 143 } 144 145 // Return whether now match the given sub-NFA. 146 template<typename _BiIter, typename _Alloc, typename _TraitsT, 147 bool __dfs_mode> 148 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_lookahead(_StateIdT __next)149 _M_lookahead(_StateIdT __next) 150 { 151 // Backreferences may refer to captured content. 152 // We may want to make this faster by not copying, 153 // but let's not be clever prematurely. 154 _ResultsVec __what(_M_cur_results); 155 _Executor __sub(_M_current, _M_end, __what, _M_re, _M_flags); 156 __sub._M_states._M_start = __next; 157 if (__sub._M_search_from_first()) 158 { 159 for (size_t __i = 0; __i < __what.size(); __i++) 160 if (__what[__i].matched) 161 _M_cur_results[__i] = __what[__i]; 162 return true; 163 } 164 return false; 165 } 166 167 // __rep_count records how many times (__rep_count.second) 168 // this node is visited under certain input iterator 169 // (__rep_count.first). This prevent the executor from entering 170 // infinite loop by refusing to continue when it's already been 171 // visited more than twice. It's `twice` instead of `once` because 172 // we need to spare one more time for potential group capture. 173 template<typename _BiIter, typename _Alloc, typename _TraitsT, 174 bool __dfs_mode> 175 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_rep_once_more(_Match_mode __match_mode,_StateIdT __i)176 _M_rep_once_more(_Match_mode __match_mode, _StateIdT __i) 177 { 178 const auto& __state = _M_nfa[__i]; 179 auto& __rep_count = _M_rep_count[__i]; 180 if (__rep_count.second == 0 || __rep_count.first != _M_current) 181 { 182 auto __back = __rep_count; 183 __rep_count.first = _M_current; 184 __rep_count.second = 1; 185 _M_dfs(__match_mode, __state._M_alt); 186 __rep_count = __back; 187 } 188 else 189 { 190 if (__rep_count.second < 2) 191 { 192 __rep_count.second++; 193 _M_dfs(__match_mode, __state._M_alt); 194 __rep_count.second--; 195 } 196 } 197 } 198 199 // _M_alt branch is "match once more", while _M_next is "get me out 200 // of this quantifier". Executing _M_next first or _M_alt first don't 201 // mean the same thing, and we need to choose the correct order under 202 // given greedy mode. 203 template<typename _BiIter, typename _Alloc, typename _TraitsT, 204 bool __dfs_mode> 205 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_handle_repeat(_Match_mode __match_mode,_StateIdT __i)206 _M_handle_repeat(_Match_mode __match_mode, _StateIdT __i) 207 { 208 const auto& __state = _M_nfa[__i]; 209 210 // Greedy. 211 if (!__state._M_neg) 212 { 213 _M_rep_once_more(__match_mode, __i); 214 // If it's DFS executor and already accepted, we're done. 215 if (!__dfs_mode || !_M_has_sol) 216 _M_dfs(__match_mode, __state._M_next); 217 } 218 else // Non-greedy mode 219 { 220 if (__dfs_mode) 221 { 222 // vice-versa. 223 _M_dfs(__match_mode, __state._M_next); 224 if (!_M_has_sol) 225 _M_rep_once_more(__match_mode, __i); 226 } 227 else 228 { 229 // DON'T attempt anything, because there's already another 230 // state with higher priority accepted. This state cannot 231 // be better by attempting its next node. 232 if (!_M_has_sol) 233 { 234 _M_dfs(__match_mode, __state._M_next); 235 // DON'T attempt anything if it's already accepted. An 236 // accepted state *must* be better than a solution that 237 // matches a non-greedy quantifier one more time. 238 if (!_M_has_sol) 239 _M_rep_once_more(__match_mode, __i); 240 } 241 } 242 } 243 } 244 245 template<typename _BiIter, typename _Alloc, typename _TraitsT, 246 bool __dfs_mode> 247 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_handle_subexpr_begin(_Match_mode __match_mode,_StateIdT __i)248 _M_handle_subexpr_begin(_Match_mode __match_mode, _StateIdT __i) 249 { 250 const auto& __state = _M_nfa[__i]; 251 252 auto& __res = _M_cur_results[__state._M_subexpr]; 253 auto __back = __res.first; 254 __res.first = _M_current; 255 _M_dfs(__match_mode, __state._M_next); 256 __res.first = __back; 257 } 258 259 template<typename _BiIter, typename _Alloc, typename _TraitsT, 260 bool __dfs_mode> 261 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_handle_subexpr_end(_Match_mode __match_mode,_StateIdT __i)262 _M_handle_subexpr_end(_Match_mode __match_mode, _StateIdT __i) 263 { 264 const auto& __state = _M_nfa[__i]; 265 266 auto& __res = _M_cur_results[__state._M_subexpr]; 267 auto __back = __res; 268 __res.second = _M_current; 269 __res.matched = true; 270 _M_dfs(__match_mode, __state._M_next); 271 __res = __back; 272 } 273 274 template<typename _BiIter, typename _Alloc, typename _TraitsT, 275 bool __dfs_mode> 276 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_handle_line_begin_assertion(_Match_mode __match_mode,_StateIdT __i)277 _M_handle_line_begin_assertion(_Match_mode __match_mode, _StateIdT __i) 278 { 279 const auto& __state = _M_nfa[__i]; 280 if (_M_at_begin()) 281 _M_dfs(__match_mode, __state._M_next); 282 } 283 284 template<typename _BiIter, typename _Alloc, typename _TraitsT, 285 bool __dfs_mode> 286 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_handle_line_end_assertion(_Match_mode __match_mode,_StateIdT __i)287 _M_handle_line_end_assertion(_Match_mode __match_mode, _StateIdT __i) 288 { 289 const auto& __state = _M_nfa[__i]; 290 if (_M_at_end()) 291 _M_dfs(__match_mode, __state._M_next); 292 } 293 294 template<typename _BiIter, typename _Alloc, typename _TraitsT, 295 bool __dfs_mode> 296 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_handle_word_boundary(_Match_mode __match_mode,_StateIdT __i)297 _M_handle_word_boundary(_Match_mode __match_mode, _StateIdT __i) 298 { 299 const auto& __state = _M_nfa[__i]; 300 if (_M_word_boundary() == !__state._M_neg) 301 _M_dfs(__match_mode, __state._M_next); 302 } 303 304 // Here __state._M_alt offers a single start node for a sub-NFA. 305 // We recursively invoke our algorithm to match the sub-NFA. 306 template<typename _BiIter, typename _Alloc, typename _TraitsT, 307 bool __dfs_mode> 308 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_handle_subexpr_lookahead(_Match_mode __match_mode,_StateIdT __i)309 _M_handle_subexpr_lookahead(_Match_mode __match_mode, _StateIdT __i) 310 { 311 const auto& __state = _M_nfa[__i]; 312 if (_M_lookahead(__state._M_alt) == !__state._M_neg) 313 _M_dfs(__match_mode, __state._M_next); 314 } 315 316 template<typename _BiIter, typename _Alloc, typename _TraitsT, 317 bool __dfs_mode> 318 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_handle_match(_Match_mode __match_mode,_StateIdT __i)319 _M_handle_match(_Match_mode __match_mode, _StateIdT __i) 320 { 321 const auto& __state = _M_nfa[__i]; 322 323 if (_M_current == _M_end) 324 return; 325 if (__dfs_mode) 326 { 327 if (__state._M_matches(*_M_current)) 328 { 329 ++_M_current; 330 _M_dfs(__match_mode, __state._M_next); 331 --_M_current; 332 } 333 } 334 else 335 if (__state._M_matches(*_M_current)) 336 _M_states._M_queue(__state._M_next, _M_cur_results); 337 } 338 339 template<typename _BiIter, typename _TraitsT> 340 struct _Backref_matcher 341 { _Backref_matcherstd::__detail::_Backref_matcher342 _Backref_matcher(bool __icase, const _TraitsT& __traits) 343 : _M_traits(__traits) { } 344 345 bool _M_applystd::__detail::_Backref_matcher346 _M_apply(_BiIter __expected_begin, 347 _BiIter __expected_end, _BiIter __actual_begin, 348 _BiIter __actual_end) 349 { 350 return _M_traits.transform(__expected_begin, __expected_end) 351 == _M_traits.transform(__actual_begin, __actual_end); 352 } 353 354 const _TraitsT& _M_traits; 355 }; 356 357 template<typename _BiIter, typename _CharT> 358 struct _Backref_matcher<_BiIter, std::regex_traits<_CharT>> 359 { 360 using _TraitsT = std::regex_traits<_CharT>; _Backref_matcherstd::__detail::_Backref_matcher361 _Backref_matcher(bool __icase, const _TraitsT& __traits) 362 : _M_icase(__icase), _M_traits(__traits) { } 363 364 bool _M_applystd::__detail::_Backref_matcher365 _M_apply(_BiIter __expected_begin, 366 _BiIter __expected_end, _BiIter __actual_begin, 367 _BiIter __actual_end) 368 { 369 if (!_M_icase) 370 return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end, 371 __actual_begin, __actual_end); 372 typedef std::ctype<_CharT> __ctype_type; 373 const auto& __fctyp = use_facet<__ctype_type>(_M_traits.getloc()); 374 return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end, 375 __actual_begin, __actual_end, 376 [this, &__fctyp](_CharT __lhs, _CharT __rhs) 377 { 378 return __fctyp.tolower(__lhs) 379 == __fctyp.tolower(__rhs); 380 }); 381 } 382 383 bool _M_icase; 384 const _TraitsT& _M_traits; 385 }; 386 387 // First fetch the matched result from _M_cur_results as __submatch; 388 // then compare it with 389 // (_M_current, _M_current + (__submatch.second - __submatch.first)). 390 // If matched, keep going; else just return and try another state. 391 template<typename _BiIter, typename _Alloc, typename _TraitsT, 392 bool __dfs_mode> 393 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_handle_backref(_Match_mode __match_mode,_StateIdT __i)394 _M_handle_backref(_Match_mode __match_mode, _StateIdT __i) 395 { 396 __glibcxx_assert(__dfs_mode); 397 398 const auto& __state = _M_nfa[__i]; 399 auto& __submatch = _M_cur_results[__state._M_backref_index]; 400 if (!__submatch.matched) 401 return; 402 auto __last = _M_current; 403 for (auto __tmp = __submatch.first; 404 __last != _M_end && __tmp != __submatch.second; 405 ++__tmp) 406 ++__last; 407 if (_Backref_matcher<_BiIter, _TraitsT>( 408 _M_re.flags() & regex_constants::icase, 409 _M_re._M_automaton->_M_traits)._M_apply( 410 __submatch.first, __submatch.second, _M_current, __last)) 411 { 412 if (__last != _M_current) 413 { 414 auto __backup = _M_current; 415 _M_current = __last; 416 _M_dfs(__match_mode, __state._M_next); 417 _M_current = __backup; 418 } 419 else 420 _M_dfs(__match_mode, __state._M_next); 421 } 422 } 423 424 template<typename _BiIter, typename _Alloc, typename _TraitsT, 425 bool __dfs_mode> 426 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_handle_accept(_Match_mode __match_mode,_StateIdT)427 _M_handle_accept(_Match_mode __match_mode, _StateIdT) 428 { 429 if _GLIBCXX17_CONSTEXPR (__dfs_mode) 430 { 431 __glibcxx_assert(!_M_has_sol); 432 if (__match_mode == _Match_mode::_Exact) 433 _M_has_sol = _M_current == _M_end; 434 else 435 _M_has_sol = true; 436 if (_M_current == _M_begin 437 && (_M_flags & regex_constants::match_not_null)) 438 _M_has_sol = false; 439 if (_M_has_sol) 440 { 441 if (_M_nfa._M_flags & regex_constants::ECMAScript) 442 _M_results = _M_cur_results; 443 else // POSIX 444 { 445 __glibcxx_assert(_M_states._M_get_sol_pos()); 446 // Here's POSIX's logic: match the longest one. However 447 // we never know which one (lhs or rhs of "|") is longer 448 // unless we try both of them and compare the results. 449 // The member variable _M_sol_pos records the end 450 // position of the last successful match. It's better 451 // to be larger, because POSIX regex is always greedy. 452 // TODO: This could be slow. 453 if (*_M_states._M_get_sol_pos() == _BiIter() 454 || std::distance(_M_begin, 455 *_M_states._M_get_sol_pos()) 456 < std::distance(_M_begin, _M_current)) 457 { 458 *_M_states._M_get_sol_pos() = _M_current; 459 _M_results = _M_cur_results; 460 } 461 } 462 } 463 } 464 else 465 { 466 if (_M_current == _M_begin 467 && (_M_flags & regex_constants::match_not_null)) 468 return; 469 if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end) 470 if (!_M_has_sol) 471 { 472 _M_has_sol = true; 473 _M_results = _M_cur_results; 474 } 475 } 476 } 477 478 template<typename _BiIter, typename _Alloc, typename _TraitsT, 479 bool __dfs_mode> 480 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_handle_alternative(_Match_mode __match_mode,_StateIdT __i)481 _M_handle_alternative(_Match_mode __match_mode, _StateIdT __i) 482 { 483 const auto& __state = _M_nfa[__i]; 484 485 if (_M_nfa._M_flags & regex_constants::ECMAScript) 486 { 487 // TODO: Fix BFS support. It is wrong. 488 _M_dfs(__match_mode, __state._M_alt); 489 // Pick lhs if it matches. Only try rhs if it doesn't. 490 if (!_M_has_sol) 491 _M_dfs(__match_mode, __state._M_next); 492 } 493 else 494 { 495 // Try both and compare the result. 496 // See "case _S_opcode_accept:" handling above. 497 _M_dfs(__match_mode, __state._M_alt); 498 auto __has_sol = _M_has_sol; 499 _M_has_sol = false; 500 _M_dfs(__match_mode, __state._M_next); 501 _M_has_sol |= __has_sol; 502 } 503 } 504 505 template<typename _BiIter, typename _Alloc, typename _TraitsT, 506 bool __dfs_mode> 507 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_dfs(_Match_mode __match_mode,_StateIdT __i)508 _M_dfs(_Match_mode __match_mode, _StateIdT __i) 509 { 510 if (_M_states._M_visited(__i)) 511 return; 512 513 switch (_M_nfa[__i]._M_opcode()) 514 { 515 case _S_opcode_repeat: 516 _M_handle_repeat(__match_mode, __i); break; 517 case _S_opcode_subexpr_begin: 518 _M_handle_subexpr_begin(__match_mode, __i); break; 519 case _S_opcode_subexpr_end: 520 _M_handle_subexpr_end(__match_mode, __i); break; 521 case _S_opcode_line_begin_assertion: 522 _M_handle_line_begin_assertion(__match_mode, __i); break; 523 case _S_opcode_line_end_assertion: 524 _M_handle_line_end_assertion(__match_mode, __i); break; 525 case _S_opcode_word_boundary: 526 _M_handle_word_boundary(__match_mode, __i); break; 527 case _S_opcode_subexpr_lookahead: 528 _M_handle_subexpr_lookahead(__match_mode, __i); break; 529 case _S_opcode_match: 530 _M_handle_match(__match_mode, __i); break; 531 case _S_opcode_backref: 532 _M_handle_backref(__match_mode, __i); break; 533 case _S_opcode_accept: 534 _M_handle_accept(__match_mode, __i); break; 535 case _S_opcode_alternative: 536 _M_handle_alternative(__match_mode, __i); break; 537 default: 538 __glibcxx_assert(false); 539 } 540 } 541 542 // Return whether now is at some word boundary. 543 template<typename _BiIter, typename _Alloc, typename _TraitsT, 544 bool __dfs_mode> 545 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: _M_word_boundary() const546 _M_word_boundary() const 547 { 548 if (_M_current == _M_begin && (_M_flags & regex_constants::match_not_bow)) 549 return false; 550 if (_M_current == _M_end && (_M_flags & regex_constants::match_not_eow)) 551 return false; 552 553 bool __left_is_word = false; 554 if (_M_current != _M_begin 555 || (_M_flags & regex_constants::match_prev_avail)) 556 { 557 auto __prev = _M_current; 558 if (_M_is_word(*std::prev(__prev))) 559 __left_is_word = true; 560 } 561 bool __right_is_word = 562 _M_current != _M_end && _M_is_word(*_M_current); 563 564 return __left_is_word != __right_is_word; 565 } 566 } // namespace __detail 567 568 _GLIBCXX_END_NAMESPACE_VERSION 569 } // namespace 570