1 // arcsum.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 to sum arcs (sum weights) in an fst.
18
19 #ifndef FST_LIB_ARCSUM_H__
20 #define FST_LIB_ARCSUM_H__
21
22 #include "fst/lib/mutable-fst.h"
23 #include "fst/lib/weight.h"
24
25 namespace fst {
26
27 template <class A>
28 class ArcSumCompare {
29 public:
operator()30 bool operator()(const A& x, const A& y) {
31 if (x.ilabel < y.ilabel) return true;
32 if (x.ilabel > y.ilabel) return false;
33 if (x.olabel < y.olabel) return true;
34 if (x.olabel < y.olabel) return false;
35 if (x.nextstate < y.nextstate) return true;
36 if (x.nextstate > y.nextstate) return false;
37 return false;
38 }
39 };
40
41
42 template <class A>
43 class ArcSumEqual {
44 public:
operator()45 bool operator()(const A& x, const A& y) {
46 return (x.ilabel == y.ilabel &&
47 x.olabel == y.olabel &&
48 x.nextstate == y.nextstate);
49 }
50 };
51
52
53 // Combines identically labeled arcs, summing weights. For each state
54 // we combine arcs with the same input and output label, summing their
55 // weights using Weight:::Plus().
56 template <class A>
ArcSum(MutableFst<A> * fst)57 void ArcSum(MutableFst<A>* fst) {
58 typedef typename A::StateId StateId;
59
60 vector<A> arcs;
61 for (StateIterator<Fst<A> > siter(*fst); !siter.Done(); siter.Next()) {
62 StateId s = siter.Value();
63 if (fst->NumArcs(s) == 0) continue;
64
65 // Sums arcs into arcs array.
66 arcs.clear();
67 arcs.reserve(fst->NumArcs(s));
68 for (ArcIterator<Fst<A> > aiter(*fst, s); !aiter.Done();
69 aiter.Next())
70 arcs.push_back(aiter.Value());
71
72 // At each state, first sorts the exiting arcs by input label, output label
73 // and destination state and then combines arcs identical in these
74 // attributes.
75 ArcSumCompare<A> comp;
76 sort(arcs.begin(), arcs.end(), comp);
77
78 // Deletes current arcs and copy in sumed arcs.
79 fst->DeleteArcs(s);
80 A current_arc = arcs[0];
81 ArcSumEqual<A> equal;
82 for (size_t i = 1; i < arcs.size(); ++i) {
83 if (equal(current_arc, arcs[i])) {
84 current_arc.weight = Plus(current_arc.weight, arcs[i].weight);
85 } else {
86 fst->AddArc(s, current_arc);
87 current_arc = arcs[i];
88 }
89 }
90 fst->AddArc(s, current_arc);
91 }
92 }
93
94 }
95
96 #endif // FST_LIB_ARCSUM_H__
97