ARPA2WFST.hpp

/*
 ARPA2WFST.hpp

 Copyright (c) [2012-], Josef Robert Novak
 All rights reserved.

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  modification, are permitted #provided that the following conditions
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    copyright notice, this list of #conditions and the following 
    disclaimer in the documentation and/or other materials provided 
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*
*/
#ifndef ARPA2WFST_H
#define ARPA2WFST_H
#include <float.h>
#include <fst/fstlib.h>
#include "util.hpp"
using namespace fst;

class ARPA2WFST {
  /*
      Transform a statistical language model in ARPA format
      to an equivalent Weighted Finite-State Acceptor.
      This implementation adopts the Google format for the output
      WFSA.  This differs from previous implementations in several ways:

       Start-state and <s> arcs:
       * There are no explicit sentence-begin (<s>) arcs
       * There is a single <s> start-state.

       Final-state and </s> arcs:
       * There are no explicit sentence-end (</s>) arcs
       * There is no explicit </s> state
       * NGrams ending in </s> are designated as final
            states, and any probability is assigned 
            to the final weight of said state.
  */  
	
public: 
  ifstream   arpa_lm_fp;
  string     arpa_lm_file;
  string     line;
  size_t     max_order;
  size_t     current_order;

  //Default values
  string     eps;      //epsilon symbol
  string     sb;       //sentence begin tag
  string     se;       //sentence end tag
  string    unk;

  //WFST stuff
  VectorFst<StdArc>  arpafst;
  SymbolTable*   ssyms;
  SymbolTable*   isyms;
  SymbolTable*   osyms;
	
  ARPA2WFST( );
  
  ARPA2WFST ( string arpa_lm, string _eps, string _sb, string _se, string _unk );
	
  void arpa_to_wfst ( );

  void phi_ify( );

private:
  double log10_2tropical( double val );
	
  void _make_arc( string istate, string ostate, string isym, double weight );

  void _make_final( string fstate, double weight );

  string _join( vector<string>::iterator start, vector<string>::iterator end );

  StdArc::Weight _get_final_bow( StdArc::StateId st );

	
};

#endif // ARPA2WFST_H //