| // rmfinalepsilon.h |
| |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| // |
| // Copyright 2005-2010 Google, Inc. |
| // Author: johans@google.com (Johan Schalkwyk) |
| // |
| // \file |
| // Function to remove of final states that have epsilon only input arcs. |
| |
| #ifndef FST_LIB_RMFINALEPSILON_H__ |
| #define FST_LIB_RMFINALEPSILON_H__ |
| |
| #include <unordered_set> |
| using std::tr1::unordered_set; |
| using std::tr1::unordered_multiset; |
| #include <vector> |
| using std::vector; |
| |
| #include <fst/connect.h> |
| #include <fst/mutable-fst.h> |
| |
| |
| namespace fst { |
| |
| template<class A> |
| void RmFinalEpsilon(MutableFst<A>* fst) { |
| typedef typename A::StateId StateId; |
| typedef typename A::Weight Weight; |
| |
| // Determine the coaccesibility of states. |
| vector<bool> access; |
| vector<bool> coaccess; |
| uint64 props = 0; |
| SccVisitor<A> scc_visitor(0, &access, &coaccess, &props); |
| DfsVisit(*fst, &scc_visitor); |
| |
| // Find potential list of removable final states. These are final states |
| // that have no outgoing transitions or final states that have a |
| // non-coaccessible future. Complexity O(S) |
| unordered_set<StateId> finals; |
| for (StateIterator<Fst<A> > siter(*fst); !siter.Done(); siter.Next()) { |
| StateId s = siter.Value(); |
| if (fst->Final(s) != Weight::Zero()) { |
| bool future_coaccess = false; |
| for (ArcIterator<Fst<A> > aiter(*fst, s); !aiter.Done(); aiter.Next()) { |
| const A& arc = aiter.Value(); |
| if (coaccess[arc.nextstate]) { |
| future_coaccess = true; |
| break; |
| } |
| } |
| if (!future_coaccess) { |
| finals.insert(s); |
| } |
| } |
| } |
| |
| // Move the final weight. Complexity O(E) |
| vector<A> arcs; |
| for (StateIterator<Fst<A> > siter(*fst); !siter.Done(); siter.Next()) { |
| StateId s = siter.Value(); |
| Weight w(fst->Final(s)); |
| |
| arcs.clear(); |
| for (ArcIterator<Fst<A> > aiter(*fst, s); !aiter.Done(); aiter.Next()) { |
| const A& arc = aiter.Value(); |
| // is next state in the list of finals |
| if (finals.find(arc.nextstate) != finals.end()) { |
| // sum up all epsilon arcs |
| if (arc.ilabel == 0 && arc.olabel == 0) { |
| w = Plus(Times(fst->Final(arc.nextstate), arc.weight), w); |
| } else { |
| arcs.push_back(arc); |
| } |
| } else { |
| arcs.push_back(arc); |
| } |
| } |
| |
| // If some arcs (epsilon arcs) were deleted, delete all |
| // arcs and add back only the non epsilon arcs |
| if (arcs.size() < fst->NumArcs(s)) { |
| fst->DeleteArcs(s); |
| fst->SetFinal(s, w); |
| for (size_t i = 0; i < arcs.size(); ++i) { |
| fst->AddArc(s, arcs[i]); |
| } |
| } |
| } |
| |
| Connect(fst); |
| } |
| |
| } // namespace fst |
| |
| #endif // FST_LIB_RMFINALEPSILON_H__ |