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// arcsum.h
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
//
// \file
// Functions to sum arcs (sum weights) in an fst.
#ifndef FST_LIB_ARCSUM_H__
#define FST_LIB_ARCSUM_H__
#include "fst/lib/mutable-fst.h"
#include "fst/lib/weight.h"
namespace fst {
template <class A>
class ArcSumCompare {
public:
bool operator()(const A& x, const A& y) {
if (x.ilabel < y.ilabel) return true;
if (x.ilabel > y.ilabel) return false;
if (x.olabel < y.olabel) return true;
if (x.olabel < y.olabel) return false;
if (x.nextstate < y.nextstate) return true;
if (x.nextstate > y.nextstate) return false;
return false;
}
};
template <class A>
class ArcSumEqual {
public:
bool operator()(const A& x, const A& y) {
return (x.ilabel == y.ilabel &&
x.olabel == y.olabel &&
x.nextstate == y.nextstate);
}
};
// Combines identically labeled arcs, summing weights. For each state
// we combine arcs with the same input and output label, summing their
// weights using Weight:::Plus().
template <class A>
void ArcSum(MutableFst<A>* fst) {
typedef typename A::StateId StateId;
vector<A> arcs;
for (StateIterator<Fst<A> > siter(*fst); !siter.Done(); siter.Next()) {
StateId s = siter.Value();
if (fst->NumArcs(s) == 0) continue;
// Sums arcs into arcs array.
arcs.clear();
arcs.reserve(fst->NumArcs(s));
for (ArcIterator<Fst<A> > aiter(*fst, s); !aiter.Done();
aiter.Next())
arcs.push_back(aiter.Value());
// At each state, first sorts the exiting arcs by input label, output label
// and destination state and then combines arcs identical in these
// attributes.
ArcSumCompare<A> comp;
sort(arcs.begin(), arcs.end(), comp);
// Deletes current arcs and copy in sumed arcs.
fst->DeleteArcs(s);
A current_arc = arcs[0];
ArcSumEqual<A> equal;
for (size_t i = 1; i < arcs.size(); ++i) {
if (equal(current_arc, arcs[i])) {
current_arc.weight = Plus(current_arc.weight, arcs[i].weight);
} else {
fst->AddArc(s, current_arc);
current_arc = arcs[i];
}
}
fst->AddArc(s, current_arc);
}
}
}
#endif // FST_LIB_ARCSUM_H__
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