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// invert.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.
//
// Copyright 2005-2010 Google, Inc.
// Author: riley@google.com (Michael Riley)
//
// \file
// Functions and classes to invert an Fst.
#ifndef FST_LIB_INVERT_H__
#define FST_LIB_INVERT_H__
#include <fst/arc-map.h>
#include <fst/mutable-fst.h>
namespace fst {
// Mapper to implement inversion of an arc.
template <class A> struct InvertMapper {
InvertMapper() {}
A operator()(const A &arc) {
return A(arc.olabel, arc.ilabel, arc.weight, arc.nextstate);
}
MapFinalAction FinalAction() const { return MAP_NO_SUPERFINAL; }
MapSymbolsAction InputSymbolsAction() const { return MAP_CLEAR_SYMBOLS; }
MapSymbolsAction OutputSymbolsAction() const { return MAP_CLEAR_SYMBOLS;}
uint64 Properties(uint64 props) { return InvertProperties(props); }
};
// Inverts the transduction corresponding to an FST by exchanging the
// FST's input and output labels. This version modifies its input.
//
// Complexity:
// - Time: O(V + E)
// - Space: O(1)
// where V = # of states and E = # of arcs.
template<class Arc> inline
void Invert(MutableFst<Arc> *fst) {
SymbolTable *input = fst->InputSymbols() ? fst->InputSymbols()->Copy() : 0;
SymbolTable *output = fst->OutputSymbols() ? fst->OutputSymbols()->Copy() : 0;
ArcMap(fst, InvertMapper<Arc>());
fst->SetInputSymbols(output);
fst->SetOutputSymbols(input);
delete input;
delete output;
}
// Inverts the transduction corresponding to an FST by exchanging the
// FST's input and output labels. This version is a delayed Fst.
//
// Complexity:
// - Time: O(v + e)
// - Space: O(1)
// where v = # of states visited, e = # of arcs visited. Constant
// time and to visit an input state or arc is assumed and exclusive
// of caching.
template <class A>
class InvertFst : public ArcMapFst<A, A, InvertMapper<A> > {
public:
typedef A Arc;
typedef InvertMapper<A> C;
typedef ArcMapFstImpl< A, A, InvertMapper<A> > Impl;
using ImplToFst<Impl>::GetImpl;
explicit InvertFst(const Fst<A> &fst) : ArcMapFst<A, A, C>(fst, C()) {
GetImpl()->SetOutputSymbols(fst.InputSymbols());
GetImpl()->SetInputSymbols(fst.OutputSymbols());
}
// See Fst<>::Copy() for doc.
InvertFst(const InvertFst<A> &fst, bool safe = false)
: ArcMapFst<A, A, C>(fst, safe) {}
// Get a copy of this InvertFst. See Fst<>::Copy() for further doc.
virtual InvertFst<A> *Copy(bool safe = false) const {
return new InvertFst(*this, safe);
}
};
// Specialization for InvertFst.
template <class A>
class StateIterator< InvertFst<A> >
: public StateIterator< ArcMapFst<A, A, InvertMapper<A> > > {
public:
explicit StateIterator(const InvertFst<A> &fst)
: StateIterator< ArcMapFst<A, A, InvertMapper<A> > >(fst) {}
};
// Specialization for InvertFst.
template <class A>
class ArcIterator< InvertFst<A> >
: public ArcIterator< ArcMapFst<A, A, InvertMapper<A> > > {
public:
ArcIterator(const InvertFst<A> &fst, typename A::StateId s)
: ArcIterator< ArcMapFst<A, A, InvertMapper<A> > >(fst, s) {}
};
// Useful alias when using StdArc.
typedef InvertFst<StdArc> StdInvertFst;
} // namespace fst
#endif // FST_LIB_INVERT_H__
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