lodr-fst.h
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// sherpa-onnx/csrc/lodr-fst.h
//
// Contains code copied from icefall/utils/ngram_lm.py
// Copyright (c) 2023 Xiaomi Corporation
//
// Copyright (c) 2025 Tilde SIA (Askars Salimbajevs)
#ifndef SHERPA_ONNX_CSRC_LODR_FST_H_
#define SHERPA_ONNX_CSRC_LODR_FST_H_
#include <memory>
#include <string>
#include <vector>
#include <optional>
#include <tuple>
#include <unordered_map>
#include <limits>
#include <algorithm>
#include <utility>
#include "kaldifst/csrc/kaldi-fst-io.h"
namespace sherpa_onnx {
struct Hypothesis;
class LodrFst {
public:
explicit LodrFst(const std::string &fst_path, int32_t backoff_id = -1);
std::pair<std::vector<int32_t>, std::vector<float>> GetNextStateCosts(
int32_t state, int32_t label);
float GetFinalCost(int32_t state);
void ComputeScore(float scale, Hypothesis *hyp, int32_t offset);
private:
fst::StdVectorFst YsToFst(const std::vector<int64_t> &ys, int32_t offset);
std::vector<std::tuple<int32_t, float>> ProcessBackoffArcs(
int32_t state, float cost);
std::optional<std::tuple<int32_t, float>> GetNextStatesCostsNoBackoff(
int32_t state, int32_t label);
int32_t FindBackoffId();
int32_t backoff_id_ = -1;
std::unique_ptr<fst::StdConstFst> fst_; // owned by this class
};
class LodrStateCost {
public:
explicit LodrStateCost(
LodrFst* fst,
const std::unordered_map<int32_t, float> &state_cost = {});
LodrStateCost ForwardOneStep(int32_t label);
float Score() const;
float FinalScore() const;
private:
// The fst_ is not owned by this class and borrowed from the caller
// (e.g. OnlineRnnLM).
LodrFst* fst_;
std::unordered_map<int32_t, float> state_cost_;
};
} // namespace sherpa_onnx
#endif // SHERPA_ONNX_CSRC_LODR_FST_H_