This class wraps a ConstArpaLm format language model with the interface defined in DeterministicOnDemandFst. More...

#include <const-arpa-lm.h>

Inheritance diagram for ConstArpaLmDeterministicFst:

Collaboration diagram for ConstArpaLmDeterministicFst:

Public Types
typedef fst::StdArc::Weight	Weight

typedef fst::StdArc::StateId	StateId

typedef fst::StdArc::Label	Label

Public Types inherited from DeterministicOnDemandFst< fst::StdArc >
typedef fst::StdArc ::StateId	StateId

typedef fst::StdArc ::Weight	Weight

typedef fst::StdArc ::Label	Label

Public Member Functions
	ConstArpaLmDeterministicFst (const ConstArpaLm &lm)

virtual StateId	Start ()

virtual Weight	Final (StateId s)

virtual bool	GetArc (StateId s, Label ilabel, fst::StdArc *oarc)

Public Member Functions inherited from DeterministicOnDemandFst< fst::StdArc >
virtual Weight	Final (StateId s)=0

virtual bool	GetArc (StateId s, Label ilabel, fst::StdArc *oarc)=0
	Note: ilabel must not be epsilon. More...

virtual	~DeterministicOnDemandFst ()

Private Types
typedef unordered_map< std::vector< Label >, StateId, VectorHasher< Label > >	MapType

Private Attributes
StateId	start_state_

MapType	wseq_to_state_

std::vector< std::vector< Label > >	state_to_wseq_

const ConstArpaLm &	lm_

Detailed Description

This class wraps a ConstArpaLm format language model with the interface defined in DeterministicOnDemandFst.

Definition at line 391 of file const-arpa-lm.h.

Member Typedef Documentation

◆ Label

typedef fst::StdArc::Label Label

Definition at line 396 of file const-arpa-lm.h.

◆ MapType

typedef unordered_map<std::vector<Label>, StateId, VectorHasher<Label> > MapType

private

Definition at line 412 of file const-arpa-lm.h.

◆ StateId

typedef fst::StdArc::StateId StateId

Definition at line 395 of file const-arpa-lm.h.

◆ Weight

typedef fst::StdArc::Weight Weight

Definition at line 394 of file const-arpa-lm.h.

Constructor & Destructor Documentation

◆ ConstArpaLmDeterministicFst()

ConstArpaLmDeterministicFst ( const ConstArpaLm & lm )

explicit

Definition at line 1013 of file const-arpa-lm.cc.

References ConstArpaLm::BosSymbol(), ConstArpaLmDeterministicFst::lm_, ConstArpaLmDeterministicFst::start_state_, ConstArpaLmDeterministicFst::state_to_wseq_, and ConstArpaLmDeterministicFst::wseq_to_state_.

                            : lm_(lm) {
   // Creates a history state for <s>.
   std::vector<Label> bos_state(1, lm_.BosSymbol());
   state_to_wseq_.push_back(bos_state);
   wseq_to_state_[bos_state] = 0;
   start_state_ = 0;
 }

Member Function Documentation

◆ Final()

fst::StdArc::Weight Final ( StateId s )

virtual

Definition at line 1022 of file const-arpa-lm.cc.

References ConstArpaLm::EosSymbol(), ConstArpaLm::GetNgramLogprob(), KALDI_ASSERT, ConstArpaLmDeterministicFst::lm_, logprob, and ConstArpaLmDeterministicFst::state_to_wseq_.

                                                             {
   // At this point, we should have created the state.
   KALDI_ASSERT(static_cast<size_t>(s) < state_to_wseq_.size());
   const std::vector<Label>& wseq = state_to_wseq_[s];
   float logprob = lm_.GetNgramLogprob(lm_.EosSymbol(), wseq);
   return Weight(-logprob);
 }

◆ GetArc()

bool GetArc	(	StateId	s,
		Label	ilabel,
		fst::StdArc *	oarc
	)

virtual

Definition at line 1030 of file const-arpa-lm.cc.

References ConstArpaLm::GetNgramLogprob(), ConstArpaLm::HistoryStateExists(), KALDI_ASSERT, ConstArpaLmDeterministicFst::lm_, logprob, ConstArpaLm::NgramOrder(), ConstArpaLmDeterministicFst::state_to_wseq_, and ConstArpaLmDeterministicFst::wseq_to_state_.

                                                                         {
   // At this point, we should have created the state.
   KALDI_ASSERT(static_cast<size_t>(s) < state_to_wseq_.size());
   std::vector<Label> wseq = state_to_wseq_[s];
 
   float logprob = lm_.GetNgramLogprob(ilabel, wseq);
   if (logprob == std::numeric_limits<float>::min()) {
     return false;
   }
 
   // Locates the next state in ConstArpaLm. Note that OOV and backoff have been
   // taken care of in ConstArpaLm.
   wseq.push_back(ilabel);
   while (wseq.size() >= lm_.NgramOrder()) {
     // History state has at most lm_.NgramOrder() -1 words in the state.
     wseq.erase(wseq.begin(), wseq.begin() + 1);
   }
   while (!lm_.HistoryStateExists(wseq)) {
     KALDI_ASSERT(wseq.size() > 0);
     wseq.erase(wseq.begin(), wseq.begin() + 1);
   }
 
   std::pair<const std::vector<Label>, StateId> wseq_state_pair(
       wseq, static_cast<Label>(state_to_wseq_.size()));
 
   // Attemps to insert the current <wseq_state_pair>. If the pair already exists
   // then it returns false.
   typedef MapType::iterator IterType;
   std::pair<IterType, bool> result = wseq_to_state_.insert(wseq_state_pair);
 
   // If the pair was just inserted, then also add it to <state_to_wseq_>.
   if (result.second == true)
     state_to_wseq_.push_back(wseq);
 
   // Creates the arc.
   oarc->ilabel = ilabel;
   oarc->olabel = ilabel;
   oarc->nextstate = result.first->second;
   oarc->weight = Weight(-logprob);
 
   return true;
 }