project.h
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// See www.openfst.org for extensive documentation on this weighted
// finite-state transducer library.
//
// Functions and classes to project an FST on to its domain or range.
#ifndef FST_PROJECT_H_
#define FST_PROJECT_H_
#include <fst/arc-map.h>
#include <fst/mutable-fst.h>
namespace fst {
// This specifies whether to project on input or output.
enum ProjectType { PROJECT_INPUT = 1, PROJECT_OUTPUT = 2 };
// Mapper to implement projection per arc.
template <class A>
class ProjectMapper {
public:
using FromArc = A;
using ToArc = A;
explicit ProjectMapper(ProjectType project_type)
: project_type_(project_type) {}
ToArc operator()(const FromArc &arc) const {
const auto label = project_type_ == PROJECT_INPUT ? arc.ilabel : arc.olabel;
return ToArc(label, label, arc.weight, arc.nextstate);
}
constexpr MapFinalAction FinalAction() const {
return MAP_NO_SUPERFINAL;
}
MapSymbolsAction InputSymbolsAction() const {
return project_type_ == PROJECT_INPUT ? MAP_COPY_SYMBOLS
: MAP_CLEAR_SYMBOLS;
}
MapSymbolsAction OutputSymbolsAction() const {
return project_type_ == PROJECT_OUTPUT ? MAP_COPY_SYMBOLS
: MAP_CLEAR_SYMBOLS;
}
uint64 Properties(uint64 props) const {
return ProjectProperties(props, project_type_ == PROJECT_INPUT);
}
private:
const ProjectType project_type_;
};
// Projects an FST onto its domain or range by either copying each arcs' input
// label to the output label or vice versa.
//
// Complexity:
//
// Time: O(V + E)
// Space: O(1)
//
// where V is the number of states and E is the number of arcs.
template <class Arc>
inline void Project(const Fst<Arc> &ifst, MutableFst<Arc> *ofst,
ProjectType project_type) {
ArcMap(ifst, ofst, ProjectMapper<Arc>(project_type));
switch (project_type) {
case PROJECT_INPUT:
ofst->SetOutputSymbols(ifst.InputSymbols());
return;
case PROJECT_OUTPUT:
ofst->SetInputSymbols(ifst.OutputSymbols());
return;
}
}
// Destructive variant of the above.
template <class Arc>
inline void Project(MutableFst<Arc> *fst, ProjectType project_type) {
ArcMap(fst, ProjectMapper<Arc>(project_type));
switch (project_type) {
case PROJECT_INPUT:
fst->SetOutputSymbols(fst->InputSymbols());
return;
case PROJECT_OUTPUT:
fst->SetInputSymbols(fst->OutputSymbols());
return;
}
}
// Projects an FST onto its domain or range by either copying each arc's input
// label to the output label or vice versa. This version is a delayed FST.
//
// Complexity:
//
// Time: O(v + e)
// Space: O(1)
//
// where v is the number of states visited and e is the number of arcs visited.
// Constant time and to visit an input state or arc is assumed and exclusive of
// caching.
template <class A>
class ProjectFst : public ArcMapFst<A, A, ProjectMapper<A>> {
public:
using FromArc = A;
using ToArc = A;
using Impl = internal::ArcMapFstImpl<A, A, ProjectMapper<A>>;
ProjectFst(const Fst<A> &fst, ProjectType project_type)
: ArcMapFst<A, A, ProjectMapper<A>>(fst, ProjectMapper<A>(project_type)) {
if (project_type == PROJECT_INPUT) {
GetMutableImpl()->SetOutputSymbols(fst.InputSymbols());
}
if (project_type == PROJECT_OUTPUT) {
GetMutableImpl()->SetInputSymbols(fst.OutputSymbols());
}
}
// See Fst<>::Copy() for doc.
ProjectFst(const ProjectFst<A> &fst, bool safe = false)
: ArcMapFst<A, A, ProjectMapper<A>>(fst, safe) {}
// Gets a copy of this ProjectFst. See Fst<>::Copy() for further doc.
ProjectFst<A> *Copy(bool safe = false) const override {
return new ProjectFst(*this, safe);
}
private:
using ImplToFst<Impl>::GetMutableImpl;
};
// Specialization for ProjectFst.
template <class A>
class StateIterator<ProjectFst<A>>
: public StateIterator<ArcMapFst<A, A, ProjectMapper<A>>> {
public:
explicit StateIterator(const ProjectFst<A> &fst)
: StateIterator<ArcMapFst<A, A, ProjectMapper<A>>>(fst) {}
};
// Specialization for ProjectFst.
template <class A>
class ArcIterator<ProjectFst<A>>
: public ArcIterator<ArcMapFst<A, A, ProjectMapper<A>>> {
public:
using StateId = typename A::StateId;
ArcIterator(const ProjectFst<A> &fst, StateId s)
: ArcIterator<ArcMapFst<A, A, ProjectMapper<A>>>(fst, s) {}
};
// Useful alias when using StdArc.
using StdProjectFst = ProjectFst<StdArc>;
} // namespace fst
#endif // FST_PROJECT_H_