src/include/fst/concat.h

// concat.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 concat of two FSTs.

#ifndef FST_LIB_CONCAT_H__
#define FST_LIB_CONCAT_H__

#include <vector>
using std::vector;
#include <algorithm>

#include <fst/mutable-fst.h>
#include <fst/rational.h>


namespace fst {

// Computes the concatenation (product) of two FSTs. If FST1
// transduces string x to y with weight a and FST2 transduces string w
// to v with weight b, then their concatenation transduces string xw
// to yv with Times(a, b).
//
// This version modifies its MutableFst argument (in first position).
//
// Complexity:
// - Time: O(V1 + V2 + E2)
// - Space: O(V1 + V2 + E2)
// where Vi = # of states and Ei = # of arcs of the ith FST.
//
template<class Arc>
void Concat(MutableFst<Arc> *fst1, const Fst<Arc> &fst2) {
  typedef typename Arc::StateId StateId;
  typedef typename Arc::Label Label;
  typedef typename Arc::Weight Weight;

  // TODO(riley): restore when voice actions issues fixed
  // Check that the symbol table are compatible
  if (!CompatSymbols(fst1->InputSymbols(), fst2.InputSymbols()) ||
      !CompatSymbols(fst1->OutputSymbols(), fst2.OutputSymbols())) {
    LOG(ERROR) << "Concat: input/output symbol tables of 1st argument "
               << "do not match input/output symbol tables of 2nd argument";
    // fst1->SetProperties(kError, kError);
    // return;
  }

  uint64 props1 = fst1->Properties(kFstProperties, false);
  uint64 props2 = fst2.Properties(kFstProperties, false);

  StateId start1 = fst1->Start();
  if (start1 == kNoStateId) {
    if (props2 & kError) fst1->SetProperties(kError, kError);
    return;
  }

  StateId numstates1 = fst1->NumStates();
  if (fst2.Properties(kExpanded, false))
    fst1->ReserveStates(numstates1 + CountStates(fst2));

  for (StateIterator< Fst<Arc> > siter2(fst2);
       !siter2.Done();
       siter2.Next()) {
    StateId s1 = fst1->AddState();
    StateId s2 = siter2.Value();
    fst1->SetFinal(s1, fst2.Final(s2));
    fst1->ReserveArcs(s1, fst2.NumArcs(s2));
    for (ArcIterator< Fst<Arc> > aiter(fst2, s2);
         !aiter.Done();
         aiter.Next()) {
      Arc arc = aiter.Value();
      arc.nextstate += numstates1;
      fst1->AddArc(s1, arc);
    }
  }

  StateId start2 = fst2.Start();
  for (StateId s1 = 0; s1 < numstates1; ++s1) {
    Weight final = fst1->Final(s1);
    if (final != Weight::Zero()) {
      fst1->SetFinal(s1, Weight::Zero());
      if (start2 != kNoStateId)
        fst1->AddArc(s1, Arc(0, 0, final, start2 + numstates1));
    }
  }
  if (start2 != kNoStateId)
    fst1->SetProperties(ConcatProperties(props1, props2), kFstProperties);
}

// Computes the concatentation of two FSTs.  This version modifies its
// MutableFst argument (in second position).
//
// Complexity:
// - Time: O(V1 + E1)
// - Space: O(V1 + E1)
// where Vi = # of states and Ei = # of arcs of the ith FST.
//
template<class Arc>
void Concat(const Fst<Arc> &fst1, MutableFst<Arc> *fst2) {
  typedef typename Arc::StateId StateId;
  typedef typename Arc::Label Label;
  typedef typename Arc::Weight Weight;

  // Check that the symbol table are compatible
  if (!CompatSymbols(fst1.InputSymbols(), fst2->InputSymbols()) ||
      !CompatSymbols(fst1.OutputSymbols(), fst2->OutputSymbols())) {
    LOG(ERROR) << "Concat: input/output symbol tables of 1st argument "
               << "do not match input/output symbol tables of 2nd argument";
    // fst2->SetProperties(kError, kError);
    // return;
  }

  uint64 props1 = fst1.Properties(kFstProperties, false);
  uint64 props2 = fst2->Properties(kFstProperties, false);

  StateId start2 = fst2->Start();
  if (start2 == kNoStateId) {
    if (props1 & kError) fst2->SetProperties(kError, kError);
    return;
  }

  StateId numstates2 = fst2->NumStates();
  if (fst1.Properties(kExpanded, false))
    fst2->ReserveStates(numstates2 + CountStates(fst1));

  for (StateIterator< Fst<Arc> > siter(fst1);
       !siter.Done();
       siter.Next()) {
    StateId s1 = siter.Value();
    StateId s2 = fst2->AddState();
    Weight final = fst1.Final(s1);
    fst2->ReserveArcs(s2, fst1.NumArcs(s1) + (final != Weight::Zero() ? 1 : 0));
    if (final != Weight::Zero())
      fst2->AddArc(s2, Arc(0, 0, final, start2));
    for (ArcIterator< Fst<Arc> > aiter(fst1, s1);
         !aiter.Done();
         aiter.Next()) {
      Arc arc = aiter.Value();
      arc.nextstate += numstates2;
      fst2->AddArc(s2, arc);
    }
  }
  StateId start1 = fst1.Start();
  fst2->SetStart(start1 == kNoStateId ? fst2->AddState() : start1 + numstates2);
  if (start1 != kNoStateId)
    fst2->SetProperties(ConcatProperties(props1, props2), kFstProperties);
}


// Computes the concatentation of two FSTs. This version modifies its
// RationalFst input (in first position).
template<class Arc>
void Concat(RationalFst<Arc> *fst1, const Fst<Arc> &fst2) {
  fst1->GetImpl()->AddConcat(fst2, true);
}

// Computes the concatentation of two FSTs. This version modifies its
// RationalFst input (in second position).
template<class Arc>
void Concat(const Fst<Arc> &fst1, RationalFst<Arc> *fst2) {
  fst2->GetImpl()->AddConcat(fst1, false);
}

typedef RationalFstOptions ConcatFstOptions;


// Computes the concatenation (product) of two FSTs; this version is a
// delayed Fst. If FST1 transduces string x to y with weight a and FST2
// transduces string w to v with weight b, then their concatenation
// transduces string xw to yv with Times(a, b).
//
// Complexity:
// - Time: O(v1 + e1 + v2 + e2),
// - Space: O(v1 + v2)
// where vi = # of states visited and ei = # of arcs visited of the
// ith FST. Constant time and space to visit an input state or arc is
// assumed and exclusive of caching.
template <class A>
class ConcatFst : public RationalFst<A> {
 public:
  using ImplToFst< RationalFstImpl<A> >::GetImpl;

  typedef A Arc;
  typedef typename A::Weight Weight;
  typedef typename A::StateId StateId;

  ConcatFst(const Fst<A> &fst1, const Fst<A> &fst2) {
    GetImpl()->InitConcat(fst1, fst2);
  }

  ConcatFst(const Fst<A> &fst1, const Fst<A> &fst2,
            const ConcatFstOptions &opts) : RationalFst<A>(opts) {
    GetImpl()->InitConcat(fst1, fst2);
  }

  // See Fst<>::Copy() for doc.
  ConcatFst(const ConcatFst<A> &fst, bool safe = false)
      : RationalFst<A>(fst, safe) {}

  // Get a copy of this ConcatFst. See Fst<>::Copy() for further doc.
  virtual ConcatFst<A> *Copy(bool safe = false) const {
    return new ConcatFst<A>(*this, safe);
  }
};


// Specialization for ConcatFst.
template <class A>
class StateIterator< ConcatFst<A> > : public StateIterator< RationalFst<A> > {
 public:
  explicit StateIterator(const ConcatFst<A> &fst)
      : StateIterator< RationalFst<A> >(fst) {}
};


// Specialization for ConcatFst.
template <class A>
class ArcIterator< ConcatFst<A> > : public ArcIterator< RationalFst<A> > {
 public:
  typedef typename A::StateId StateId;

  ArcIterator(const ConcatFst<A> &fst, StateId s)
      : ArcIterator< RationalFst<A> >(fst, s) {}
};


// Useful alias when using StdArc.
typedef ConcatFst<StdArc> StdConcatFst;

}  // namespace fst

#endif  // FST_LIB_CONCAT_H__