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
28 namespace fst {
29
30 // Mapper to implement inversion of an arc.
31 template <class A> struct InvertMapper {
InvertMapperInvertMapper32 InvertMapper() {}
33
operatorInvertMapper34 A operator()(const A &arc) {
35 return A(arc.olabel, arc.ilabel, arc.weight, arc.nextstate);
36 }
37
FinalActionInvertMapper38 MapFinalAction FinalAction() const { return MAP_NO_SUPERFINAL; }
39
InputSymbolsActionInvertMapper40 MapSymbolsAction InputSymbolsAction() const { return MAP_CLEAR_SYMBOLS; }
41
OutputSymbolsActionInvertMapper42 MapSymbolsAction OutputSymbolsAction() const { return MAP_CLEAR_SYMBOLS;}
43
PropertiesInvertMapper44 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.
55 template<class Arc> inline
Invert(MutableFst<Arc> * fst)56 void 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.
76 template <class A>
77 class 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
InvertFst(const Fst<A> & fst)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.
101 template <class A>
102 class StateIterator< InvertFst<A> >
103 : public StateIterator< ArcMapFst<A, A, InvertMapper<A> > > {
104 public:
StateIterator(const InvertFst<A> & fst)105 explicit StateIterator(const InvertFst<A> &fst)
106 : StateIterator< ArcMapFst<A, A, InvertMapper<A> > >(fst) {}
107 };
108
109
110 // Specialization for InvertFst.
111 template <class A>
112 class ArcIterator< InvertFst<A> >
113 : public ArcIterator< ArcMapFst<A, A, InvertMapper<A> > > {
114 public:
ArcIterator(const InvertFst<A> & fst,typename A::StateId s)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.
121 typedef InvertFst<StdArc> StdInvertFst;
122
123 } // namespace fst
124
125 #endif // FST_LIB_INVERT_H__
126