epsnormalize.h
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// See www.openfst.org for extensive documentation on this weighted
// finite-state transducer library.
//
// Function that implements epsilon-normalization.
#ifndef FST_EPSNORMALIZE_H_
#define FST_EPSNORMALIZE_H_
#include <fst/arc-map.h>
#include <fst/factor-weight.h>
#include <fst/invert.h>
#include <fst/rmepsilon.h>
namespace fst {
enum EpsNormalizeType { EPS_NORM_INPUT, EPS_NORM_OUTPUT };
// Returns an equivalent FST that is epsilon-normalized. An acceptor is
// epsilon-normalized if it is epsilon-removed. A transducer is input
// epsilon-normalized if additionally if on each path any epsilon input
// label follows all non-epsilon input labels. Output epsilon-normalized
// is defined similarly.
//
// For more information, see:
//
// Mohri, M. 2002. Generic epsilon-removal and input epsilon-normalization
// algorithms for weighted transducers. International Journal of Computer
// Science, 13(1): 129-143, 2002.
template <class Arc>
void EpsNormalize(const Fst<Arc> &ifst, MutableFst<Arc> *ofst,
EpsNormalizeType type = EPS_NORM_INPUT) {
EpsNormalize<Arc, GALLIC>(ifst, ofst, type);
}
// Same as above, expect allows specifying explicitely the gallic weight type.
template <class Arc, GallicType G>
void EpsNormalize(const Fst<Arc> &ifst, MutableFst<Arc> *ofst,
EpsNormalizeType type) {
VectorFst<GallicArc<Arc, G>> gfst;
if (type == EPS_NORM_INPUT) {
ArcMap(ifst, &gfst, ToGallicMapper<Arc, G>());
} else { // type == EPS_NORM_OUTPUT
ArcMap(InvertFst<Arc>(ifst), &gfst, ToGallicMapper<Arc, G>());
}
RmEpsilon(&gfst);
FactorWeightFst<GallicArc<Arc, G>,
GallicFactor<typename Arc::Label, typename Arc::Weight, G>>
fwfst(gfst);
ArcMap(fwfst, ofst, FromGallicMapper<Arc, G>());
ofst->SetOutputSymbols(ifst.OutputSymbols());
if (type == EPS_NORM_OUTPUT) Invert(ofst);
}
} // namespace fst
#endif // FST_EPSNORMALIZE_H_