// closure.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 compute the concatenative closure of an Fst.
#ifndef FST_LIB_CLOSURE_H__
#define FST_LIB_CLOSURE_H__
#include <vector>
using std::vector;
#include <algorithm>
#include <fst/mutable-fst.h>
#include <fst/rational.h>
namespace fst {
// Computes the concatenative closure. This version modifies its
// MutableFst input. If FST transduces string x to y with weight a,
// then the closure transduces x to y with weight a, xx to yy with
// weight Times(a, a), xxx to yyy with with Times(Times(a, a), a),
// etc. If closure_type == CLOSURE_STAR, then the empty string is
// transduced to itself with weight Weight::One() as well.
//
// Complexity:
// - Time: O(V)
// - Space: O(V)
// where V = # of states.
template<class Arc>
void Closure(MutableFst<Arc> *fst, ClosureType closure_type) {
typedef typename Arc::StateId StateId;
typedef typename Arc::Label Label;
typedef typename Arc::Weight Weight;
uint64 props = fst->Properties(kFstProperties, false);
StateId start = fst->Start();
for (StateIterator< MutableFst<Arc> > siter(*fst);
!siter.Done();
siter.Next()) {
StateId s = siter.Value();
Weight final = fst->Final(s);
if (final != Weight::Zero())
fst->AddArc(s, Arc(0, 0, final, start));
}
if (closure_type == CLOSURE_STAR) {
fst->ReserveStates(fst->NumStates() + 1);
StateId nstart = fst->AddState();
fst->SetStart(nstart);
fst->SetFinal(nstart, Weight::One());
if (start != kNoLabel)
fst->AddArc(nstart, Arc(0, 0, Weight::One(), start));
}
fst->SetProperties(ClosureProperties(props, closure_type == CLOSURE_STAR),
kFstProperties);
}
// Computes the concatenative closure. This version modifies its
// RationalFst input.
template<class Arc>
void Closure(RationalFst<Arc> *fst, ClosureType closure_type) {
fst->GetImpl()->AddClosure(closure_type);
}
struct ClosureFstOptions : RationalFstOptions {
ClosureType type;
ClosureFstOptions(const RationalFstOptions &opts, ClosureType t)
: RationalFstOptions(opts), type(t) {}
explicit ClosureFstOptions(ClosureType t) : type(t) {}
ClosureFstOptions() : type(CLOSURE_STAR) {}
};
// Computes the concatenative closure. This version is a delayed
// Fst. If FST transduces string x to y with weight a, then the
// closure transduces x to y with weight a, xx to yy with weight
// Times(a, a), xxx to yyy with weight Times(Times(a, a), a), etc. If
// closure_type == CLOSURE_STAR, then The empty string is transduced
// to itself with weight Weight::One() as well.
//
// Complexity:
// - Time: O(v)
// - Space: O(v)
// where v = # of states visited. Constant time and space to visit an
// input state or arc is assumed and exclusive of caching.
template <class A>
class ClosureFst : public RationalFst<A> {
public:
using ImplToFst< RationalFstImpl<A> >::GetImpl;
typedef A Arc;
ClosureFst(const Fst<A> &fst, ClosureType closure_type) {
GetImpl()->InitClosure(fst, closure_type);
}
ClosureFst(const Fst<A> &fst, const ClosureFstOptions &opts)
: RationalFst<A>(opts) {
GetImpl()->InitClosure(fst, opts.type);
}
// See Fst<>::Copy() for doc.
ClosureFst(const ClosureFst<A> &fst, bool safe = false)
: RationalFst<A>(fst, safe) {}
// Get a copy of this ClosureFst. See Fst<>::Copy() for further doc.
virtual ClosureFst<A> *Copy(bool safe = false) const {
return new ClosureFst<A>(*this, safe);
}
};
// Specialization for ClosureFst.
template <class A>
class StateIterator< ClosureFst<A> > : public StateIterator< RationalFst<A> > {
public:
explicit StateIterator(const ClosureFst<A> &fst)
: StateIterator< RationalFst<A> >(fst) {}
};
// Specialization for ClosureFst.
template <class A>
class ArcIterator< ClosureFst<A> > : public ArcIterator< RationalFst<A> > {
public:
typedef typename A::StateId StateId;
ArcIterator(const ClosureFst<A> &fst, StateId s)
: ArcIterator< RationalFst<A> >(fst, s) {}
};
// Useful alias when using StdArc.
typedef ClosureFst<StdArc> StdClosureFst;
} // namespace fst
#endif // FST_LIB_CLOSURE_H__