1 // compose.h 2 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 // 15 // Copyright 2005-2010 Google, Inc. 16 // Author: riley (at) google.com (Michael Riley) 17 // 18 // \file 19 // Class to compute the composition of two FSTs 20 21 #ifndef FST_LIB_COMPOSE_H__ 22 #define FST_LIB_COMPOSE_H__ 23 24 #include <algorithm> 25 #include <string> 26 #include <vector> 27 using std::vector; 28 29 #include <fst/cache.h> 30 #include <fst/compose-filter.h> 31 #include <fst/lookahead-filter.h> 32 #include <fst/matcher.h> 33 #include <fst/state-table.h> 34 #include <fst/test-properties.h> 35 36 37 namespace fst { 38 39 // Delayed composition options templated on the arc type, the matcher, 40 // the composition filter, and the composition state table. By 41 // default, the matchers, filter, and state table are constructed by 42 // composition. If set below, the user can instead pass in these 43 // objects; in that case, ComposeFst takes their ownership. This 44 // version controls composition implemented between generic Fst<Arc> 45 // types and a shared matcher type M for Fst<Arc>. This should be 46 // adequate for most applications, giving a reasonable tradeoff 47 // between efficiency and code sharing (but see ComposeFstImplOptions). 48 template <class A, 49 class M = Matcher<Fst<A> >, 50 class F = SequenceComposeFilter<M>, 51 class T = GenericComposeStateTable<A, typename F::FilterState> > 52 struct ComposeFstOptions : public CacheOptions { 53 M *matcher1; // FST1 matcher (see matcher.h) 54 M *matcher2; // FST2 matcher 55 F *filter; // Composition filter (see compose-filter.h) 56 T *state_table; // Composition state table (see compose-state-table.h) 57 58 explicit ComposeFstOptions(const CacheOptions &opts, 59 M *mat1 = 0, M *mat2 = 0, 60 F *filt = 0, T *sttable= 0) 61 : CacheOptions(opts), matcher1(mat1), matcher2(mat2), 62 filter(filt), state_table(sttable) {} 63 64 ComposeFstOptions() : matcher1(0), matcher2(0), filter(0), state_table(0) {} 65 }; 66 67 68 // Delayed composition options templated on the two matcher types, the 69 // composition filter, and the composition state table. By default, 70 // the matchers, filter, and state table are constructed by 71 // composition. If set below, the user can instead pass in these 72 // objects; in that case, ComposeFst takes their ownership. This 73 // version controls composition implemented using arbitrary matchers 74 // (of the same Arc type but otherwise arbitrary Fst type). The user 75 // must ensure the matchers are compatible. These options permit the 76 // most efficient use, but shares the least code. This is for advanced 77 // use only in the most demanding or specialized applications that can 78 // benefit from it (o.w. prefer ComposeFstOptions). 79 template <class M1, class M2, 80 class F = SequenceComposeFilter<M1, M2>, 81 class T = GenericComposeStateTable<typename M1::Arc, 82 typename F::FilterState> > 83 struct ComposeFstImplOptions : public CacheOptions { 84 M1 *matcher1; // FST1 matcher (see matcher.h) 85 M2 *matcher2; // FST2 matcher 86 F *filter; // Composition filter (see compose-filter.h) 87 T *state_table; // Composition state table (see compose-state-table.h) 88 89 explicit ComposeFstImplOptions(const CacheOptions &opts, 90 M1 *mat1 = 0, M2 *mat2 = 0, 91 F *filt = 0, T *sttable= 0) 92 : CacheOptions(opts), matcher1(mat1), matcher2(mat2), 93 filter(filt), state_table(sttable) {} 94 95 ComposeFstImplOptions() 96 : matcher1(0), matcher2(0), filter(0), state_table(0) {} 97 }; 98 99 100 // Implementation of delayed composition. This base class is 101 // common to the variants with different matchers, composition filters 102 // and state tables. 103 template <class A> 104 class ComposeFstImplBase : public CacheImpl<A> { 105 public: 106 using FstImpl<A>::SetType; 107 using FstImpl<A>::SetProperties; 108 using FstImpl<A>::Properties; 109 using FstImpl<A>::SetInputSymbols; 110 using FstImpl<A>::SetOutputSymbols; 111 112 using CacheBaseImpl< CacheState<A> >::HasStart; 113 using CacheBaseImpl< CacheState<A> >::HasFinal; 114 using CacheBaseImpl< CacheState<A> >::HasArcs; 115 using CacheBaseImpl< CacheState<A> >::SetFinal; 116 using CacheBaseImpl< CacheState<A> >::SetStart; 117 118 typedef typename A::Label Label; 119 typedef typename A::Weight Weight; 120 typedef typename A::StateId StateId; 121 typedef CacheState<A> State; 122 123 ComposeFstImplBase(const Fst<A> &fst1, const Fst<A> &fst2, 124 const CacheOptions &opts) 125 :CacheImpl<A>(opts) { 126 VLOG(2) << "ComposeFst(" << this << "): Begin"; 127 SetType("compose"); 128 129 if (!CompatSymbols(fst2.InputSymbols(), fst1.OutputSymbols())) { 130 FSTERROR() << "ComposeFst: output symbol table of 1st argument " 131 << "does not match input symbol table of 2nd argument"; 132 SetProperties(kError, kError); 133 } 134 135 SetInputSymbols(fst1.InputSymbols()); 136 SetOutputSymbols(fst2.OutputSymbols()); 137 } 138 139 ComposeFstImplBase(const ComposeFstImplBase<A> &impl) 140 : CacheImpl<A>(impl) { 141 SetProperties(impl.Properties(), kCopyProperties); 142 SetInputSymbols(impl.InputSymbols()); 143 SetOutputSymbols(impl.OutputSymbols()); 144 } 145 146 virtual ComposeFstImplBase<A> *Copy() = 0; 147 148 virtual ~ComposeFstImplBase() {} 149 150 StateId Start() { 151 if (!HasStart()) { 152 StateId start = ComputeStart(); 153 if (start != kNoStateId) { 154 SetStart(start); 155 } 156 } 157 return CacheImpl<A>::Start(); 158 } 159 160 Weight Final(StateId s) { 161 if (!HasFinal(s)) { 162 Weight final = ComputeFinal(s); 163 SetFinal(s, final); 164 } 165 return CacheImpl<A>::Final(s); 166 } 167 168 virtual void Expand(StateId s) = 0; 169 170 size_t NumArcs(StateId s) { 171 if (!HasArcs(s)) 172 Expand(s); 173 return CacheImpl<A>::NumArcs(s); 174 } 175 176 size_t NumInputEpsilons(StateId s) { 177 if (!HasArcs(s)) 178 Expand(s); 179 return CacheImpl<A>::NumInputEpsilons(s); 180 } 181 182 size_t NumOutputEpsilons(StateId s) { 183 if (!HasArcs(s)) 184 Expand(s); 185 return CacheImpl<A>::NumOutputEpsilons(s); 186 } 187 188 void InitArcIterator(StateId s, ArcIteratorData<A> *data) { 189 if (!HasArcs(s)) 190 Expand(s); 191 CacheImpl<A>::InitArcIterator(s, data); 192 } 193 194 protected: 195 virtual StateId ComputeStart() = 0; 196 virtual Weight ComputeFinal(StateId s) = 0; 197 }; 198 199 200 // Implementaion of delayed composition templated on the matchers (see 201 // matcher.h), composition filter (see compose-filter-inl.h) and 202 // the composition state table (see compose-state-table.h). 203 template <class M1, class M2, class F, class T> 204 class ComposeFstImpl : public ComposeFstImplBase<typename M1::Arc> { 205 typedef typename M1::FST FST1; 206 typedef typename M2::FST FST2; 207 typedef typename M1::Arc Arc; 208 typedef typename Arc::StateId StateId; 209 typedef typename Arc::Label Label; 210 typedef typename Arc::Weight Weight; 211 typedef typename F::FilterState FilterState; 212 typedef typename F::Matcher1 Matcher1; 213 typedef typename F::Matcher2 Matcher2; 214 215 using CacheBaseImpl<CacheState<Arc> >::SetArcs; 216 using FstImpl<Arc>::SetType; 217 using FstImpl<Arc>::SetProperties; 218 219 typedef ComposeStateTuple<StateId, FilterState> StateTuple; 220 221 public: 222 ComposeFstImpl(const FST1 &fst1, const FST2 &fst2, 223 const ComposeFstImplOptions<M1, M2, F, T> &opts); 224 225 ComposeFstImpl(const ComposeFstImpl<M1, M2, F, T> &impl) 226 : ComposeFstImplBase<Arc>(impl), 227 filter_(new F(*impl.filter_, true)), 228 matcher1_(filter_->GetMatcher1()), 229 matcher2_(filter_->GetMatcher2()), 230 fst1_(matcher1_->GetFst()), 231 fst2_(matcher2_->GetFst()), 232 state_table_(new T(*impl.state_table_)), 233 match_type_(impl.match_type_) {} 234 235 ~ComposeFstImpl() { 236 VLOG(2) << "ComposeFst(" << this 237 << "): End: # of visited states: " << state_table_->Size(); 238 239 delete filter_; 240 delete state_table_; 241 } 242 243 virtual ComposeFstImpl<M1, M2, F, T> *Copy() { 244 return new ComposeFstImpl<M1, M2, F, T>(*this); 245 } 246 247 uint64 Properties() const { return Properties(kFstProperties); } 248 249 // Set error if found; return FST impl properties. 250 uint64 Properties(uint64 mask) const { 251 if ((mask & kError) && 252 (fst1_.Properties(kError, false) || 253 fst2_.Properties(kError, false) || 254 (matcher1_->Properties(0) & kError) || 255 (matcher2_->Properties(0) & kError) | 256 (filter_->Properties(0) & kError) || 257 state_table_->Error())) { 258 SetProperties(kError, kError); 259 } 260 return FstImpl<Arc>::Properties(mask); 261 } 262 263 // Arranges it so that the first arg to OrderedExpand is the Fst 264 // that will be matched on. 265 void Expand(StateId s) { 266 const StateTuple &tuple = state_table_->Tuple(s); 267 StateId s1 = tuple.state_id1; 268 StateId s2 = tuple.state_id2; 269 filter_->SetState(s1, s2, tuple.filter_state); 270 if (match_type_ == MATCH_OUTPUT || 271 (match_type_ == MATCH_BOTH && 272 internal::NumArcs(fst1_, s1) > internal::NumArcs(fst2_, s2))) 273 OrderedExpand(s, fst1_, s1, fst2_, s2, matcher1_, false); 274 else 275 OrderedExpand(s, fst2_, s2, fst1_, s1, matcher2_, true); 276 } 277 278 private: 279 // This does that actual matching of labels in the composition. The 280 // arguments are ordered so matching is called on state 'sa' of 281 // 'fsta' for each arc leaving state 'sb' of 'fstb'. The 'match_input' arg 282 // determines whether the input or output label of arcs at 'sb' is 283 // the one to match on. 284 template <class FST, class Matcher> 285 void OrderedExpand(StateId s, const Fst<Arc> &, StateId sa, 286 const FST &fstb, StateId sb, 287 Matcher *matchera, bool match_input) { 288 matchera->SetState(sa); 289 290 // First process non-consuming symbols (e.g., epsilons) on FSTA. 291 Arc loop(match_input ? 0 : kNoLabel, match_input ? kNoLabel : 0, 292 Weight::One(), sb); 293 MatchArc(s, matchera, loop, match_input); 294 295 // Then process matches on FSTB. 296 for (ArcIterator<FST> iterb(fstb, sb); !iterb.Done(); iterb.Next()) 297 MatchArc(s, matchera, iterb.Value(), match_input); 298 299 SetArcs(s); 300 } 301 302 // Matches a single transition from 'fstb' against 'fata' at 's'. 303 template <class Matcher> 304 void MatchArc(StateId s, Matcher *matchera, 305 const Arc &arc, bool match_input) { 306 if (matchera->Find(match_input ? arc.olabel : arc.ilabel)) { 307 for (; !matchera->Done(); matchera->Next()) { 308 Arc arca = matchera->Value(); 309 Arc arcb = arc; 310 if (match_input) { 311 const FilterState &f = filter_->FilterArc(&arcb, &arca); 312 if (f != FilterState::NoState()) 313 AddArc(s, arcb, arca, f); 314 } else { 315 const FilterState &f = filter_->FilterArc(&arca, &arcb); 316 if (f != FilterState::NoState()) 317 AddArc(s, arca, arcb, f); 318 } 319 } 320 } 321 } 322 323 // Add a matching transition at 's'. 324 void AddArc(StateId s, const Arc &arc1, const Arc &arc2, 325 const FilterState &f) { 326 StateTuple tuple(arc1.nextstate, arc2.nextstate, f); 327 Arc oarc(arc1.ilabel, arc2.olabel, Times(arc1.weight, arc2.weight), 328 state_table_->FindState(tuple)); 329 CacheImpl<Arc>::PushArc(s, oarc); 330 } 331 332 StateId ComputeStart() { 333 StateId s1 = fst1_.Start(); 334 if (s1 == kNoStateId) 335 return kNoStateId; 336 337 StateId s2 = fst2_.Start(); 338 if (s2 == kNoStateId) 339 return kNoStateId; 340 341 const FilterState &f = filter_->Start(); 342 StateTuple tuple(s1, s2, f); 343 return state_table_->FindState(tuple); 344 } 345 346 Weight ComputeFinal(StateId s) { 347 const StateTuple &tuple = state_table_->Tuple(s); 348 StateId s1 = tuple.state_id1; 349 Weight final1 = internal::Final(fst1_, s1); 350 if (final1 == Weight::Zero()) 351 return final1; 352 353 StateId s2 = tuple.state_id2; 354 Weight final2 = internal::Final(fst2_, s2); 355 if (final2 == Weight::Zero()) 356 return final2; 357 358 filter_->SetState(s1, s2, tuple.filter_state); 359 filter_->FilterFinal(&final1, &final2); 360 return Times(final1, final2); 361 } 362 363 F *filter_; 364 Matcher1 *matcher1_; 365 Matcher2 *matcher2_; 366 const FST1 &fst1_; 367 const FST2 &fst2_; 368 T *state_table_; 369 370 MatchType match_type_; 371 372 void operator=(const ComposeFstImpl<M1, M2, F, T> &); // disallow 373 }; 374 375 template <class M1, class M2, class F, class T> inline 376 ComposeFstImpl<M1, M2, F, T>::ComposeFstImpl( 377 const FST1 &fst1, const FST2 &fst2, 378 const ComposeFstImplOptions<M1, M2, F, T> &opts) 379 : ComposeFstImplBase<Arc>(fst1, fst2, opts), 380 filter_(opts.filter ? opts.filter : 381 new F(fst1, fst2, opts.matcher1, opts.matcher2)), 382 matcher1_(filter_->GetMatcher1()), 383 matcher2_(filter_->GetMatcher2()), 384 fst1_(matcher1_->GetFst()), 385 fst2_(matcher2_->GetFst()), 386 state_table_(opts.state_table ? opts.state_table : 387 new T(fst1_, fst2_)) { 388 MatchType type1 = matcher1_->Type(false); 389 MatchType type2 = matcher2_->Type(false); 390 if (type1 == MATCH_OUTPUT && type2 == MATCH_INPUT) { 391 match_type_ = MATCH_BOTH; 392 } else if (type1 == MATCH_OUTPUT) { 393 match_type_ = MATCH_OUTPUT; 394 } else if (type2 == MATCH_INPUT) { 395 match_type_ = MATCH_INPUT; 396 } else if (matcher1_->Type(true) == MATCH_OUTPUT) { 397 match_type_ = MATCH_OUTPUT; 398 } else if (matcher2_->Type(true) == MATCH_INPUT) { 399 match_type_ = MATCH_INPUT; 400 } else { 401 FSTERROR() << "ComposeFst: 1st argument cannot match on output labels " 402 << "and 2nd argument cannot match on input labels (sort?)."; 403 SetProperties(kError, kError); 404 } 405 uint64 fprops1 = fst1.Properties(kFstProperties, false); 406 uint64 fprops2 = fst2.Properties(kFstProperties, false); 407 uint64 mprops1 = matcher1_->Properties(fprops1); 408 uint64 mprops2 = matcher2_->Properties(fprops2); 409 uint64 cprops = ComposeProperties(mprops1, mprops2); 410 SetProperties(filter_->Properties(cprops), kCopyProperties); 411 if (state_table_->Error()) SetProperties(kError, kError); 412 VLOG(2) << "ComposeFst(" << this << "): Initialized"; 413 } 414 415 416 // Computes the composition of two transducers. This version is a 417 // delayed Fst. If FST1 transduces string x to y with weight a and FST2 418 // transduces y to z with weight b, then their composition transduces 419 // string x to z with weight Times(x, z). 420 // 421 // The output labels of the first transducer or the input labels of 422 // the second transducer must be sorted (with the default matcher). 423 // The weights need to form a commutative semiring (valid for 424 // TropicalWeight and LogWeight). 425 // 426 // Complexity: 427 // Assuming the first FST is unsorted and the second is sorted: 428 // - Time: O(v1 v2 d1 (log d2 + m2)), 429 // - Space: O(v1 v2) 430 // where vi = # of states visited, di = maximum out-degree, and mi the 431 // maximum multiplicity of the states visited for the ith 432 // FST. Constant time and space to visit an input state or arc is 433 // assumed and exclusive of caching. 434 // 435 // Caveats: 436 // - ComposeFst does not trim its output (since it is a delayed operation). 437 // - The efficiency of composition can be strongly affected by several factors: 438 // - the choice of which tnansducer is sorted - prefer sorting the FST 439 // that has the greater average out-degree. 440 // - the amount of non-determinism 441 // - the presence and location of epsilon transitions - avoid epsilon 442 // transitions on the output side of the first transducer or 443 // the input side of the second transducer or prefer placing 444 // them later in a path since they delay matching and can 445 // introduce non-coaccessible states and transitions. 446 // 447 // This class attaches interface to implementation and handles 448 // reference counting, delegating most methods to ImplToFst. 449 template <class A> 450 class ComposeFst : public ImplToFst< ComposeFstImplBase<A> > { 451 public: 452 friend class ArcIterator< ComposeFst<A> >; 453 friend class StateIterator< ComposeFst<A> >; 454 455 typedef A Arc; 456 typedef typename A::Weight Weight; 457 typedef typename A::StateId StateId; 458 typedef CacheState<A> State; 459 typedef ComposeFstImplBase<A> Impl; 460 461 using ImplToFst<Impl>::SetImpl; 462 463 // Compose specifying only caching options. 464 ComposeFst(const Fst<A> &fst1, const Fst<A> &fst2, 465 const CacheOptions &opts = CacheOptions()) 466 : ImplToFst<Impl>(CreateBase(fst1, fst2, opts)) {} 467 468 // Compose specifying one shared matcher type M. Requires input 469 // Fsts and matcher FST type (M::FST) be Fst<A>. Recommended for 470 // best code-sharing and matcher compatiblity. 471 template <class M, class F, class T> 472 ComposeFst(const Fst<A> &fst1, const Fst<A> &fst2, 473 const ComposeFstOptions<A, M, F, T> &opts) 474 : ImplToFst<Impl>(CreateBase1(fst1, fst2, opts)) {} 475 476 // Compose specifying two matcher types M1 and M2. Requires input 477 // Fsts (of the same Arc type but o.w. arbitrary) match the 478 // corresponding matcher FST types (M1::FST, M2::FST). Recommended 479 // only for advanced use in demanding or specialized applications 480 // due to potential code bloat and matcher incompatibilities. 481 template <class M1, class M2, class F, class T> 482 ComposeFst(const typename M1::FST &fst1, const typename M2::FST &fst2, 483 const ComposeFstImplOptions<M1, M2, F, T> &opts) 484 : ImplToFst<Impl>(CreateBase2(fst1, fst2, opts)) {} 485 486 // See Fst<>::Copy() for doc. 487 ComposeFst(const ComposeFst<A> &fst, bool safe = false) { 488 if (safe) 489 SetImpl(fst.GetImpl()->Copy()); 490 else 491 SetImpl(fst.GetImpl(), false); 492 } 493 494 // Get a copy of this ComposeFst. See Fst<>::Copy() for further doc. 495 virtual ComposeFst<A> *Copy(bool safe = false) const { 496 return new ComposeFst<A>(*this, safe); 497 } 498 499 virtual inline void InitStateIterator(StateIteratorData<A> *data) const; 500 501 virtual void InitArcIterator(StateId s, ArcIteratorData<A> *data) const { 502 GetImpl()->InitArcIterator(s, data); 503 } 504 505 protected: 506 ComposeFst() {} 507 508 // Create compose implementation specifying two matcher types. 509 template <class M1, class M2, class F, class T> 510 static Impl *CreateBase2( 511 const typename M1::FST &fst1, const typename M2::FST &fst2, 512 const ComposeFstImplOptions<M1, M2, F, T> &opts) { 513 Impl *impl = new ComposeFstImpl<M1, M2, F, T>(fst1, fst2, opts); 514 if (!(Weight::Properties() & kCommutative)) { 515 int64 props1 = fst1.Properties(kUnweighted, true); 516 int64 props2 = fst2.Properties(kUnweighted, true); 517 if (!(props1 & kUnweighted) && !(props2 & kUnweighted)) { 518 FSTERROR() << "ComposeFst: Weights must be a commutative semiring: " 519 << Weight::Type(); 520 impl->SetProperties(kError, kError); 521 } 522 } 523 return impl; 524 } 525 526 // Create compose implementation specifying one matcher type. 527 // Requires input Fsts and matcher FST type (M::FST) be Fst<A> 528 template <class M, class F, class T> 529 static Impl *CreateBase1(const Fst<A> &fst1, const Fst<A> &fst2, 530 const ComposeFstOptions<A, M, F, T> &opts) { 531 ComposeFstImplOptions<M, M, F, T> nopts(opts, opts.matcher1, opts.matcher2, 532 opts.filter, opts.state_table); 533 return CreateBase2(fst1, fst2, nopts); 534 } 535 536 // Create compose implementation specifying no matcher type. 537 static Impl *CreateBase(const Fst<A> &fst1, const Fst<A> &fst2, 538 const CacheOptions &opts) { 539 switch (LookAheadMatchType(fst1, fst2)) { // Check for lookahead matchers 540 default: 541 case MATCH_NONE: { // Default composition (no look-ahead) 542 ComposeFstOptions<Arc> nopts(opts); 543 return CreateBase1(fst1, fst2, nopts); 544 } 545 case MATCH_OUTPUT: { // Lookahead on fst1 546 typedef typename DefaultLookAhead<Arc, MATCH_OUTPUT>::FstMatcher M; 547 typedef typename DefaultLookAhead<Arc, MATCH_OUTPUT>::ComposeFilter F; 548 ComposeFstOptions<Arc, M, F> nopts(opts); 549 return CreateBase1(fst1, fst2, nopts); 550 } 551 case MATCH_INPUT: { // Lookahead on fst2 552 typedef typename DefaultLookAhead<Arc, MATCH_INPUT>::FstMatcher M; 553 typedef typename DefaultLookAhead<Arc, MATCH_INPUT>::ComposeFilter F; 554 ComposeFstOptions<Arc, M, F> nopts(opts); 555 return CreateBase1(fst1, fst2, nopts); 556 } 557 } 558 } 559 560 private: 561 // Makes visible to friends. 562 Impl *GetImpl() const { return ImplToFst<Impl>::GetImpl(); } 563 564 void operator=(const ComposeFst<A> &fst); // disallow 565 }; 566 567 568 // Specialization for ComposeFst. 569 template<class A> 570 class StateIterator< ComposeFst<A> > 571 : public CacheStateIterator< ComposeFst<A> > { 572 public: 573 explicit StateIterator(const ComposeFst<A> &fst) 574 : CacheStateIterator< ComposeFst<A> >(fst, fst.GetImpl()) {} 575 }; 576 577 578 // Specialization for ComposeFst. 579 template <class A> 580 class ArcIterator< ComposeFst<A> > 581 : public CacheArcIterator< ComposeFst<A> > { 582 public: 583 typedef typename A::StateId StateId; 584 585 ArcIterator(const ComposeFst<A> &fst, StateId s) 586 : CacheArcIterator< ComposeFst<A> >(fst.GetImpl(), s) { 587 if (!fst.GetImpl()->HasArcs(s)) 588 fst.GetImpl()->Expand(s); 589 } 590 591 private: 592 DISALLOW_COPY_AND_ASSIGN(ArcIterator); 593 }; 594 595 template <class A> inline 596 void ComposeFst<A>::InitStateIterator(StateIteratorData<A> *data) const { 597 data->base = new StateIterator< ComposeFst<A> >(*this); 598 } 599 600 // Useful alias when using StdArc. 601 typedef ComposeFst<StdArc> StdComposeFst; 602 603 enum ComposeFilter { AUTO_FILTER, SEQUENCE_FILTER, ALT_SEQUENCE_FILTER, 604 MATCH_FILTER }; 605 606 struct ComposeOptions { 607 bool connect; // Connect output 608 ComposeFilter filter_type; // Which pre-defined filter to use 609 610 ComposeOptions(bool c, ComposeFilter ft = AUTO_FILTER) 611 : connect(c), filter_type(ft) {} 612 ComposeOptions() : connect(true), filter_type(AUTO_FILTER) {} 613 }; 614 615 // Computes the composition of two transducers. This version writes 616 // the composed FST into a MurableFst. If FST1 transduces string x to 617 // y with weight a and FST2 transduces y to z with weight b, then 618 // their composition transduces string x to z with weight 619 // Times(x, z). 620 // 621 // The output labels of the first transducer or the input labels of 622 // the second transducer must be sorted. The weights need to form a 623 // commutative semiring (valid for TropicalWeight and LogWeight). 624 // 625 // Complexity: 626 // Assuming the first FST is unsorted and the second is sorted: 627 // - Time: O(V1 V2 D1 (log D2 + M2)), 628 // - Space: O(V1 V2 D1 M2) 629 // where Vi = # of states, Di = maximum out-degree, and Mi is 630 // the maximum multiplicity for the ith FST. 631 // 632 // Caveats: 633 // - Compose trims its output. 634 // - The efficiency of composition can be strongly affected by several factors: 635 // - the choice of which tnansducer is sorted - prefer sorting the FST 636 // that has the greater average out-degree. 637 // - the amount of non-determinism 638 // - the presence and location of epsilon transitions - avoid epsilon 639 // transitions on the output side of the first transducer or 640 // the input side of the second transducer or prefer placing 641 // them later in a path since they delay matching and can 642 // introduce non-coaccessible states and transitions. 643 template<class Arc> 644 void Compose(const Fst<Arc> &ifst1, const Fst<Arc> &ifst2, 645 MutableFst<Arc> *ofst, 646 const ComposeOptions &opts = ComposeOptions()) { 647 typedef Matcher< Fst<Arc> > M; 648 649 if (opts.filter_type == AUTO_FILTER) { 650 CacheOptions nopts; 651 nopts.gc_limit = 0; // Cache only the last state for fastest copy. 652 *ofst = ComposeFst<Arc>(ifst1, ifst2, nopts); 653 } else if (opts.filter_type == SEQUENCE_FILTER) { 654 ComposeFstOptions<Arc> copts; 655 copts.gc_limit = 0; // Cache only the last state for fastest copy. 656 *ofst = ComposeFst<Arc>(ifst1, ifst2, copts); 657 } else if (opts.filter_type == ALT_SEQUENCE_FILTER) { 658 ComposeFstOptions<Arc, M, AltSequenceComposeFilter<M> > copts; 659 copts.gc_limit = 0; // Cache only the last state for fastest copy. 660 *ofst = ComposeFst<Arc>(ifst1, ifst2, copts); 661 } else if (opts.filter_type == MATCH_FILTER) { 662 ComposeFstOptions<Arc, M, MatchComposeFilter<M> > copts; 663 copts.gc_limit = 0; // Cache only the last state for fastest copy. 664 *ofst = ComposeFst<Arc>(ifst1, ifst2, copts); 665 } 666 667 if (opts.connect) 668 Connect(ofst); 669 } 670 671 } // namespace fst 672 673 #endif // FST_LIB_COMPOSE_H__ 674