ArithmeticModel.h

Go to the documentation of this file.

 
#pragma once
 
#include <stdexcept>
#include <alib/map>
#include <alib/set>
 
template < class SymbolType >
class ArithmeticModel {
    ext::map < SymbolType, unsigned > m_high_cumulative_frequency;
    unsigned m_global_high; // EOF is with probability 1/n (ie its low is m_global_high - 1 and hight is m_global_high) with cumulative frequency right below the m_global_high
 
public:
    ArithmeticModel ( const ext::set < SymbolType > & alphabet ) {
        unsigned frequency = 0;
        for ( const SymbolType & symbol : alphabet )
            m_high_cumulative_frequency.insert ( std::make_pair ( symbol, ++ frequency ) );
        m_global_high = frequency + 1;
    }
 
    void update ( const SymbolType & symbol ) {
        for ( auto i = m_high_cumulative_frequency.find ( symbol ); i != m_high_cumulative_frequency.end ( ) ; ++ i )
            i->second += 1;
        m_global_high += 1;
    }
 
    void getProbability ( const SymbolType & c, unsigned & low_prob, unsigned & high_prob ) const {
        auto i = m_high_cumulative_frequency.find ( c );
        high_prob = i->second;
        low_prob = 0;
 
        if ( i != m_high_cumulative_frequency.begin ( ) )
            low_prob = std::prev ( i )->second;
    }
 
    void getProbabilityEof ( unsigned & low_prob, unsigned & high_prob ) const {
        low_prob = m_global_high - 1;
        high_prob = m_global_high;
    }
 
    SymbolType getChar ( unsigned scaled_value, unsigned & low_prob, unsigned & high_prob ) const {
        for ( auto i = m_high_cumulative_frequency.begin ( ); i != m_high_cumulative_frequency.end ( ); ++ i )
            if ( scaled_value < i->second ) {
                high_prob = i->second;
                low_prob = 0;
 
                if ( i != m_high_cumulative_frequency.begin ( ) )
                    low_prob = std::prev ( i )->second;
 
                return i->first;
            }
        throw std::logic_error("error");
    }
 
    bool isEof ( unsigned scaled_value ) const {
        return scaled_value == m_global_high - 1;
    }
 
    unsigned getCount ( ) const {
        return m_global_high;
    }
 
};