arcsum.h revision 4a68b3365c8c50aa93505e99ead2565ab73dcdb0 
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
25namespace fst {
26
27template <class A>
28class ArcSumCompare {
29 public:
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
42template <class A>
43class ArcSumEqual {
44 public:
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().
56template <class A>
57void 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