1 // project.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 //
16 // \file
17 // Functions and classes to project an Fst on to its domain or range.
18
19 #ifndef FST_LIB_PROJECT_H__
20 #define FST_LIB_PROJECT_H__
21
22 #include "fst/lib/map.h"
23 #include "fst/lib/mutable-fst.h"
24
25 namespace fst {
26
27 // This specifies whether to project on input or output.
28 enum ProjectType { PROJECT_INPUT = 1, PROJECT_OUTPUT = 2 };
29
30
31 // Mapper to implement projection per arc.
32 template <class A> class ProjectMapper {
33 public:
ProjectMapper(ProjectType project_type)34 explicit ProjectMapper(ProjectType project_type)
35 : project_type_(project_type) {}
36
operator()37 A operator()(const A &arc) {
38 typename A::Label label = project_type_ == PROJECT_INPUT
39 ? arc.ilabel : arc.olabel;
40 return A(label, label, arc.weight, arc.nextstate);
41 }
42
Properties(uint64 props)43 uint64 Properties(uint64 props) {
44 return ProjectProperties(props, project_type_ == PROJECT_INPUT);
45 }
46
FinalAction()47 MapFinalAction FinalAction() const { return MAP_NO_SUPERFINAL; }
48
49 private:
50 ProjectType project_type_;
51 };
52
53
54 // Projects an FST onto its domain or range by either copying each arcs'
55 // input label to the output label or vice versa. This version modifies
56 // its input.
57 //
58 // Complexity:
59 // - Time: O(V + E)
60 // - Space: O(1)
61 // where V = # of states and E = # of arcs.
62 template<class Arc> inline
Project(MutableFst<Arc> * fst,ProjectType project_type)63 void Project(MutableFst<Arc> *fst, ProjectType project_type) {
64 Map(fst, ProjectMapper<Arc>(project_type));
65 }
66
67
68 // Projects an FST onto its domain or range by either copying each arc's
69 // input label to the output label or vice versa. This version is a delayed
70 // Fst.
71 //
72 // Complexity:
73 // - Time: O(v + e)
74 // - Space: O(1)
75 // where v = # of states visited, e = # of arcs visited. Constant
76 // time and to visit an input state or arc is assumed and exclusive
77 // of caching.
78 template <class A>
79 class ProjectFst : public MapFst<A, A, ProjectMapper<A> > {
80 public:
81 typedef A Arc;
82 typedef ProjectMapper<A> C;
83
ProjectFst(const Fst<A> & fst,ProjectType project_type)84 ProjectFst(const Fst<A> &fst, ProjectType project_type)
85 : MapFst<A, A, C>(fst, C(project_type)) {}
86
ProjectFst(const ProjectFst<A> & fst)87 ProjectFst(const ProjectFst<A> &fst) : MapFst<A, A, C>(fst) {}
88
Copy()89 virtual ProjectFst<A> *Copy() const { return new ProjectFst(*this); }
90 };
91
92
93 // Specialization for ProjectFst.
94 template <class A>
95 class StateIterator< ProjectFst<A> >
96 : public StateIterator< MapFst<A, A, ProjectMapper<A> > > {
97 public:
StateIterator(const ProjectFst<A> & fst)98 explicit StateIterator(const ProjectFst<A> &fst)
99 : StateIterator< MapFst<A, A, ProjectMapper<A> > >(fst) {}
100 };
101
102
103 // Specialization for ProjectFst.
104 template <class A>
105 class ArcIterator< ProjectFst<A> >
106 : public ArcIterator< MapFst<A, A, ProjectMapper<A> > > {
107 public:
ArcIterator(const ProjectFst<A> & fst,typename A::StateId s)108 ArcIterator(const ProjectFst<A> &fst, typename A::StateId s)
109 : ArcIterator< MapFst<A, A, ProjectMapper<A> > >(fst, s) {}
110 };
111
112
113 // Useful alias when using StdArc.
114 typedef ProjectFst<StdArc> StdProjectFst;
115
116 } // namespace fst
117
118 #endif // FST_LIB_PROJECT_H__
119