1// invert.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@google.com (Michael Riley) 17// 18// \file 19// Functions and classes to invert an Fst. 20 21#ifndef FST_LIB_INVERT_H__ 22#define FST_LIB_INVERT_H__ 23 24#include <fst/arc-map.h> 25#include <fst/mutable-fst.h> 26 27 28namespace fst { 29 30// Mapper to implement inversion of an arc. 31template <class A> struct InvertMapper { 32 InvertMapper() {} 33 34 A operator()(const A &arc) { 35 return A(arc.olabel, arc.ilabel, arc.weight, arc.nextstate); 36 } 37 38 MapFinalAction FinalAction() const { return MAP_NO_SUPERFINAL; } 39 40 MapSymbolsAction InputSymbolsAction() const { return MAP_CLEAR_SYMBOLS; } 41 42 MapSymbolsAction OutputSymbolsAction() const { return MAP_CLEAR_SYMBOLS;} 43 44 uint64 Properties(uint64 props) { return InvertProperties(props); } 45}; 46 47 48// Inverts the transduction corresponding to an FST by exchanging the 49// FST's input and output labels. This version modifies its input. 50// 51// Complexity: 52// - Time: O(V + E) 53// - Space: O(1) 54// where V = # of states and E = # of arcs. 55template<class Arc> inline 56void Invert(MutableFst<Arc> *fst) { 57 SymbolTable *input = fst->InputSymbols() ? fst->InputSymbols()->Copy() : 0; 58 SymbolTable *output = fst->OutputSymbols() ? fst->OutputSymbols()->Copy() : 0; 59 ArcMap(fst, InvertMapper<Arc>()); 60 fst->SetInputSymbols(output); 61 fst->SetOutputSymbols(input); 62 delete input; 63 delete output; 64} 65 66 67// Inverts the transduction corresponding to an FST by exchanging the 68// FST's input and output labels. This version is a delayed Fst. 69// 70// Complexity: 71// - Time: O(v + e) 72// - Space: O(1) 73// where v = # of states visited, e = # of arcs visited. Constant 74// time and to visit an input state or arc is assumed and exclusive 75// of caching. 76template <class A> 77class InvertFst : public ArcMapFst<A, A, InvertMapper<A> > { 78 public: 79 typedef A Arc; 80 typedef InvertMapper<A> C; 81 typedef ArcMapFstImpl< A, A, InvertMapper<A> > Impl; 82 using ImplToFst<Impl>::GetImpl; 83 84 explicit InvertFst(const Fst<A> &fst) : ArcMapFst<A, A, C>(fst, C()) { 85 GetImpl()->SetOutputSymbols(fst.InputSymbols()); 86 GetImpl()->SetInputSymbols(fst.OutputSymbols()); 87 } 88 89 // See Fst<>::Copy() for doc. 90 InvertFst(const InvertFst<A> &fst, bool safe = false) 91 : ArcMapFst<A, A, C>(fst, safe) {} 92 93 // Get a copy of this InvertFst. See Fst<>::Copy() for further doc. 94 virtual InvertFst<A> *Copy(bool safe = false) const { 95 return new InvertFst(*this, safe); 96 } 97}; 98 99 100// Specialization for InvertFst. 101template <class A> 102class StateIterator< InvertFst<A> > 103 : public StateIterator< ArcMapFst<A, A, InvertMapper<A> > > { 104 public: 105 explicit StateIterator(const InvertFst<A> &fst) 106 : StateIterator< ArcMapFst<A, A, InvertMapper<A> > >(fst) {} 107}; 108 109 110// Specialization for InvertFst. 111template <class A> 112class ArcIterator< InvertFst<A> > 113 : public ArcIterator< ArcMapFst<A, A, InvertMapper<A> > > { 114 public: 115 ArcIterator(const InvertFst<A> &fst, typename A::StateId s) 116 : ArcIterator< ArcMapFst<A, A, InvertMapper<A> > >(fst, s) {} 117}; 118 119 120// Useful alias when using StdArc. 121typedef InvertFst<StdArc> StdInvertFst; 122 123} // namespace fst 124 125#endif // FST_LIB_INVERT_H__ 126