1 // class template regex -*- C++ -*- 2 3 // Copyright (C) 2013-2018 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>:: 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(_StateIdT __next) 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 = __next; 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>:: 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 // _M_alt branch is "match once more", while _M_next is "get me out 199 // of this quantifier". Executing _M_next first or _M_alt first don't 200 // mean the same thing, and we need to choose the correct order under 201 // given greedy mode. 202 template<typename _BiIter, typename _Alloc, typename _TraitsT, 203 bool __dfs_mode> 204 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 205 _M_handle_repeat(_Match_mode __match_mode, _StateIdT __i) 206 { 207 const auto& __state = _M_nfa[__i]; 208 209 // Greedy. 210 if (!__state._M_neg) 211 { 212 _M_rep_once_more(__match_mode, __i); 213 // If it's DFS executor and already accepted, we're done. 214 if (!__dfs_mode || !_M_has_sol) 215 _M_dfs(__match_mode, __state._M_next); 216 } 217 else // Non-greedy mode 218 { 219 if (__dfs_mode) 220 { 221 // vice-versa. 222 _M_dfs(__match_mode, __state._M_next); 223 if (!_M_has_sol) 224 _M_rep_once_more(__match_mode, __i); 225 } 226 else 227 { 228 // DON'T attempt anything, because there's already another 229 // state with higher priority accepted. This state cannot 230 // be better by attempting its next node. 231 if (!_M_has_sol) 232 { 233 _M_dfs(__match_mode, __state._M_next); 234 // DON'T attempt anything if it's already accepted. An 235 // accepted state *must* be better than a solution that 236 // matches a non-greedy quantifier one more time. 237 if (!_M_has_sol) 238 _M_rep_once_more(__match_mode, __i); 239 } 240 } 241 } 242 } 243 244 template<typename _BiIter, typename _Alloc, typename _TraitsT, 245 bool __dfs_mode> 246 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 247 _M_handle_subexpr_begin(_Match_mode __match_mode, _StateIdT __i) 248 { 249 const auto& __state = _M_nfa[__i]; 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 } 257 258 template<typename _BiIter, typename _Alloc, typename _TraitsT, 259 bool __dfs_mode> 260 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 261 _M_handle_subexpr_end(_Match_mode __match_mode, _StateIdT __i) 262 { 263 const auto& __state = _M_nfa[__i]; 264 265 auto& __res = _M_cur_results[__state._M_subexpr]; 266 auto __back = __res; 267 __res.second = _M_current; 268 __res.matched = true; 269 _M_dfs(__match_mode, __state._M_next); 270 __res = __back; 271 } 272 273 template<typename _BiIter, typename _Alloc, typename _TraitsT, 274 bool __dfs_mode> 275 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 276 _M_handle_line_begin_assertion(_Match_mode __match_mode, _StateIdT __i) 277 { 278 const auto& __state = _M_nfa[__i]; 279 if (_M_at_begin()) 280 _M_dfs(__match_mode, __state._M_next); 281 } 282 283 template<typename _BiIter, typename _Alloc, typename _TraitsT, 284 bool __dfs_mode> 285 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 286 _M_handle_line_end_assertion(_Match_mode __match_mode, _StateIdT __i) 287 { 288 const auto& __state = _M_nfa[__i]; 289 if (_M_at_end()) 290 _M_dfs(__match_mode, __state._M_next); 291 } 292 293 template<typename _BiIter, typename _Alloc, typename _TraitsT, 294 bool __dfs_mode> 295 inline void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 296 _M_handle_word_boundary(_Match_mode __match_mode, _StateIdT __i) 297 { 298 const auto& __state = _M_nfa[__i]; 299 if (_M_word_boundary() == !__state._M_neg) 300 _M_dfs(__match_mode, __state._M_next); 301 } 302 303 // Here __state._M_alt offers a single start node for a sub-NFA. 304 // We recursively invoke our algorithm to match the sub-NFA. 305 template<typename _BiIter, typename _Alloc, typename _TraitsT, 306 bool __dfs_mode> 307 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 308 _M_handle_subexpr_lookahead(_Match_mode __match_mode, _StateIdT __i) 309 { 310 const auto& __state = _M_nfa[__i]; 311 if (_M_lookahead(__state._M_alt) == !__state._M_neg) 312 _M_dfs(__match_mode, __state._M_next); 313 } 314 315 template<typename _BiIter, typename _Alloc, typename _TraitsT, 316 bool __dfs_mode> 317 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 318 _M_handle_match(_Match_mode __match_mode, _StateIdT __i) 319 { 320 const auto& __state = _M_nfa[__i]; 321 322 if (_M_current == _M_end) 323 return; 324 if (__dfs_mode) 325 { 326 if (__state._M_matches(*_M_current)) 327 { 328 ++_M_current; 329 _M_dfs(__match_mode, __state._M_next); 330 --_M_current; 331 } 332 } 333 else 334 if (__state._M_matches(*_M_current)) 335 _M_states._M_queue(__state._M_next, _M_cur_results); 336 } 337 338 template<typename _BiIter, typename _TraitsT> 339 struct _Backref_matcher 340 { 341 _Backref_matcher(bool __icase, const _TraitsT& __traits) 342 : _M_traits(__traits) { } 343 344 bool 345 _M_apply(_BiIter __expected_begin, 346 _BiIter __expected_end, _BiIter __actual_begin, 347 _BiIter __actual_end) 348 { 349 return _M_traits.transform(__expected_begin, __expected_end) 350 == _M_traits.transform(__actual_begin, __actual_end); 351 } 352 353 const _TraitsT& _M_traits; 354 }; 355 356 template<typename _BiIter, typename _CharT> 357 struct _Backref_matcher<_BiIter, std::regex_traits<_CharT>> 358 { 359 using _TraitsT = std::regex_traits<_CharT>; 360 _Backref_matcher(bool __icase, const _TraitsT& __traits) 361 : _M_icase(__icase), _M_traits(__traits) { } 362 363 bool 364 _M_apply(_BiIter __expected_begin, 365 _BiIter __expected_end, _BiIter __actual_begin, 366 _BiIter __actual_end) 367 { 368 if (!_M_icase) 369 return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end, 370 __actual_begin, __actual_end); 371 typedef std::ctype<_CharT> __ctype_type; 372 const auto& __fctyp = use_facet<__ctype_type>(_M_traits.getloc()); 373 return _GLIBCXX_STD_A::__equal4(__expected_begin, __expected_end, 374 __actual_begin, __actual_end, 375 [this, &__fctyp](_CharT __lhs, _CharT __rhs) 376 { 377 return __fctyp.tolower(__lhs) 378 == __fctyp.tolower(__rhs); 379 }); 380 } 381 382 bool _M_icase; 383 const _TraitsT& _M_traits; 384 }; 385 386 // First fetch the matched result from _M_cur_results as __submatch; 387 // then compare it with 388 // (_M_current, _M_current + (__submatch.second - __submatch.first)). 389 // If matched, keep going; else just return and try another state. 390 template<typename _BiIter, typename _Alloc, typename _TraitsT, 391 bool __dfs_mode> 392 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 393 _M_handle_backref(_Match_mode __match_mode, _StateIdT __i) 394 { 395 __glibcxx_assert(__dfs_mode); 396 397 const auto& __state = _M_nfa[__i]; 398 auto& __submatch = _M_cur_results[__state._M_backref_index]; 399 if (!__submatch.matched) 400 return; 401 auto __last = _M_current; 402 for (auto __tmp = __submatch.first; 403 __last != _M_end && __tmp != __submatch.second; 404 ++__tmp) 405 ++__last; 406 if (_Backref_matcher<_BiIter, _TraitsT>( 407 _M_re.flags() & regex_constants::icase, 408 _M_re._M_automaton->_M_traits)._M_apply( 409 __submatch.first, __submatch.second, _M_current, __last)) 410 { 411 if (__last != _M_current) 412 { 413 auto __backup = _M_current; 414 _M_current = __last; 415 _M_dfs(__match_mode, __state._M_next); 416 _M_current = __backup; 417 } 418 else 419 _M_dfs(__match_mode, __state._M_next); 420 } 421 } 422 423 template<typename _BiIter, typename _Alloc, typename _TraitsT, 424 bool __dfs_mode> 425 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 426 _M_handle_accept(_Match_mode __match_mode, _StateIdT __i) 427 { 428 if (__dfs_mode) 429 { 430 __glibcxx_assert(!_M_has_sol); 431 if (__match_mode == _Match_mode::_Exact) 432 _M_has_sol = _M_current == _M_end; 433 else 434 _M_has_sol = true; 435 if (_M_current == _M_begin 436 && (_M_flags & regex_constants::match_not_null)) 437 _M_has_sol = false; 438 if (_M_has_sol) 439 { 440 if (_M_nfa._M_flags & regex_constants::ECMAScript) 441 _M_results = _M_cur_results; 442 else // POSIX 443 { 444 __glibcxx_assert(_M_states._M_get_sol_pos()); 445 // Here's POSIX's logic: match the longest one. However 446 // we never know which one (lhs or rhs of "|") is longer 447 // unless we try both of them and compare the results. 448 // The member variable _M_sol_pos records the end 449 // position of the last successful match. It's better 450 // to be larger, because POSIX regex is always greedy. 451 // TODO: This could be slow. 452 if (*_M_states._M_get_sol_pos() == _BiIter() 453 || std::distance(_M_begin, 454 *_M_states._M_get_sol_pos()) 455 < std::distance(_M_begin, _M_current)) 456 { 457 *_M_states._M_get_sol_pos() = _M_current; 458 _M_results = _M_cur_results; 459 } 460 } 461 } 462 } 463 else 464 { 465 if (_M_current == _M_begin 466 && (_M_flags & regex_constants::match_not_null)) 467 return; 468 if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end) 469 if (!_M_has_sol) 470 { 471 _M_has_sol = true; 472 _M_results = _M_cur_results; 473 } 474 } 475 } 476 477 template<typename _BiIter, typename _Alloc, typename _TraitsT, 478 bool __dfs_mode> 479 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 480 _M_handle_alternative(_Match_mode __match_mode, _StateIdT __i) 481 { 482 const auto& __state = _M_nfa[__i]; 483 484 if (_M_nfa._M_flags & regex_constants::ECMAScript) 485 { 486 // TODO: Fix BFS support. It is wrong. 487 _M_dfs(__match_mode, __state._M_alt); 488 // Pick lhs if it matches. Only try rhs if it doesn't. 489 if (!_M_has_sol) 490 _M_dfs(__match_mode, __state._M_next); 491 } 492 else 493 { 494 // Try both and compare the result. 495 // See "case _S_opcode_accept:" handling above. 496 _M_dfs(__match_mode, __state._M_alt); 497 auto __has_sol = _M_has_sol; 498 _M_has_sol = false; 499 _M_dfs(__match_mode, __state._M_next); 500 _M_has_sol |= __has_sol; 501 } 502 } 503 504 template<typename _BiIter, typename _Alloc, typename _TraitsT, 505 bool __dfs_mode> 506 void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 507 _M_dfs(_Match_mode __match_mode, _StateIdT __i) 508 { 509 if (_M_states._M_visited(__i)) 510 return; 511 512 switch (_M_nfa[__i]._M_opcode()) 513 { 514 case _S_opcode_repeat: 515 _M_handle_repeat(__match_mode, __i); break; 516 case _S_opcode_subexpr_begin: 517 _M_handle_subexpr_begin(__match_mode, __i); break; 518 case _S_opcode_subexpr_end: 519 _M_handle_subexpr_end(__match_mode, __i); break; 520 case _S_opcode_line_begin_assertion: 521 _M_handle_line_begin_assertion(__match_mode, __i); break; 522 case _S_opcode_line_end_assertion: 523 _M_handle_line_end_assertion(__match_mode, __i); break; 524 case _S_opcode_word_boundary: 525 _M_handle_word_boundary(__match_mode, __i); break; 526 case _S_opcode_subexpr_lookahead: 527 _M_handle_subexpr_lookahead(__match_mode, __i); break; 528 case _S_opcode_match: 529 _M_handle_match(__match_mode, __i); break; 530 case _S_opcode_backref: 531 _M_handle_backref(__match_mode, __i); break; 532 case _S_opcode_accept: 533 _M_handle_accept(__match_mode, __i); break; 534 case _S_opcode_alternative: 535 _M_handle_alternative(__match_mode, __i); break; 536 default: 537 __glibcxx_assert(false); 538 } 539 } 540 541 // Return whether now is at some word boundary. 542 template<typename _BiIter, typename _Alloc, typename _TraitsT, 543 bool __dfs_mode> 544 bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>:: 545 _M_word_boundary() const 546 { 547 if (_M_current == _M_begin && (_M_flags & regex_constants::match_not_bow)) 548 return false; 549 if (_M_current == _M_end && (_M_flags & regex_constants::match_not_eow)) 550 return false; 551 552 bool __left_is_word = false; 553 if (_M_current != _M_begin 554 || (_M_flags & regex_constants::match_prev_avail)) 555 { 556 auto __prev = _M_current; 557 if (_M_is_word(*std::prev(__prev))) 558 __left_is_word = true; 559 } 560 bool __right_is_word = 561 _M_current != _M_end && _M_is_word(*_M_current); 562 563 return __left_is_word != __right_is_word; 564 } 565 } // namespace __detail 566 567 _GLIBCXX_END_NAMESPACE_VERSION 568 } // namespace 569