///functor: Run composition itself, separate from load times (e.g. which may include an fst expansion).
VectorFst<Arc> * operator() () {
if (!fst_.NumStates() ) {
LWARN ("Empty lattice. ... Skipping LM application!");
return NULL;
}
while ( qc_.size() ) {
StateId s = qc_.front();
qc_.pop();
pair<StateId, const typename KenLMModelT::State> p = get ( s );
StateId& s1 = p.first;
const typename KenLMModelT::State s2 = p.second;
for ( ArcIterator< VectorFst<Arc> > arc1 ( fst_, s1 ); !arc1.Done();
arc1.Next() ) {
const Arc& a1 = arc1.Value();
float w = 0;
float wp = wp_;
typename KenLMModelT::State nextlmstate;
if ( epsilons_.find ( a1.olabel ) == epsilons_.end() ) {
w = lmmodel_.Score ( s2, idbridge_.map (a1.olabel), nextlmstate ) * natlog10_;
//silly hack
if ( a1.olabel <= 2 ) {
wp = 0;
if (a1.olabel == 1 ) w = 0; //get same result as srilm
}
} else {
nextlmstate = s2;
wp = 0; //We don't count epsilon labels
}
pair<StateId, bool> nextp = add ( nextlmstate
, a1.nextstate
, fst_.Final ( a1.nextstate ) );
StateId& newstate = nextp.first;
bool visited = nextp.second;
composed_->AddArc ( s
, Arc ( a1.ilabel, a1.olabel
, Times ( a1.weight, Times (mw_ ( w ) , mw_ (wp) ) )
, newstate ) );
//Finally, only add newstate to the queue if it hasn't been visited previously
if ( !visited ) {
qc_.push ( newstate );
}
}
}
LINFO ( "Done! Number of states=" << composed_->NumStates() );
return composed_;
};
/**
* Constructor. Initializes on-the-fly composition with a language model.
* \param fst Machine you want to apply the language to. Pass a delayed machine if you can, as it will expand it in constructor.
* \param model A KenLM language model
* \param epsilons List of words to work as epsilons
* \param natlog Use or not natural logs
* \param lmscale Language model scale
*/
ApplyLanguageModelOnTheFly ( const Fst<Arc>& fst,
KenLMModelT& model,
#ifndef USE_GOOGLE_SPARSE_HASH
unordered_set<Label>& epsilons,
#else
google::dense_hash_set<Label>& epsilons,
#endif
bool natlog,
float lmscale ,
float lmwp,
const IdBridgeT& idbridge
) :
composed_ ( NULL ) ,
natlog10_ ( natlog ? -lmscale* ::log ( 10.0 ) : -lmscale ),
fst_ ( fst ),
lmmodel_ ( model ),
vocab_ ( model.GetVocabulary() ),
wp_ ( lmwp ) ,
epsilons_ ( epsilons ) ,
history ( model.Order(), 0),
idbridge_ (idbridge) {
#ifdef USE_GOOGLE_SPARSE_HASH
stateexistence_.set_empty_key ( numeric_limits<ull>::max() );
statemap_.set_empty_key ( numeric_limits<uint64_t>::max() );
basic_string<unsigned> aux (KENLM_MAX_ORDER, numeric_limits<unsigned>::max() );
seenlmstates_.set_empty_key ( aux );
#endif
buffersize = ( model.Order() - 1 ) * sizeof ( unsigned int );
buffer = const_cast<unsigned *> ( history.c_str() );
if (!fst_.NumStates() ) {
LWARN ("Empty lattice");
return;
}
composed_ = new VectorFst<Arc>;
typename KenLMModelT::State bs = model.NullContextState();
///Initialize with first state
pair<StateId, bool> nextp = add ( bs, fst_.Start(),
fst_.Final ( fst_.Start() ) );
qc_.push ( nextp.first );
composed_->SetStart ( nextp.first );
};
