dlibs/dlib/entropy_encoder/entropy_encoder_kernel_2.cpp

// Copyright (C) 2004  Davis E. King ([email protected])
// License: Boost Software License   See LICENSE.txt for the full license.
#ifndef DLIB_ENTROPY_ENCODER_KERNEL_2_CPp_
#define DLIB_ENTROPY_ENCODER_KERNEL_2_CPp_
#include "entropy_encoder_kernel_2.h"
#include <iostream>
#include <streambuf>

namespace dlib
{


// ----------------------------------------------------------------------------------------

    entropy_encoder_kernel_2::
    entropy_encoder_kernel_2(
    ) :
        initial_low(0x00000001),
        initial_high(0xffffffff),
        out(0),
        low(initial_low),
        high(initial_high)
    {
    }

// ----------------------------------------------------------------------------------------

    entropy_encoder_kernel_2::
    ~entropy_encoder_kernel_2 (
    )
    {
        try {
            if (out != 0)
            {
                flush();
            }
        } catch (...) {}
    }

// ----------------------------------------------------------------------------------------

    void entropy_encoder_kernel_2::
    clear(
    )
    {
        if (out != 0)
        {
            flush();
        }
        out = 0;
    }

// ----------------------------------------------------------------------------------------

    void entropy_encoder_kernel_2::
    set_stream (
        std::ostream& out_
    )
    {
        if (out != 0)
        {
            // if a stream is currently set then flush the buffers to it before
            // we switch to the new stream
            flush();
        }
    
        out = &out_;
        streambuf = out_.rdbuf();

        // reset the encoder state
        low = initial_low;
        high = initial_high;
    }

// ----------------------------------------------------------------------------------------

    bool entropy_encoder_kernel_2::
    stream_is_set (
    ) const
    {
        if (out != 0)
            return true;
        else
            return false;
    }

// ----------------------------------------------------------------------------------------

    std::ostream& entropy_encoder_kernel_2::
    get_stream (
    ) const
    {
        return *out;
    }

// ----------------------------------------------------------------------------------------

    void entropy_encoder_kernel_2::
    encode (
        uint32 low_count,
        uint32 high_count,
        uint32 total
    )
    {
        // note that we must add one because of the convention that
        // high == the real upper range minus 1
        uint32 r = (high-low+1)/total;                 

        // note that we must subtract 1 to preserve the convention that
        // high == the real upper range - 1
        high = low + r*high_count-1;
        low = low + r*low_count;



        while (true )
        {

            // if high and low don't have the same 8 high order bits
            if ((high&0xFF000000) != (low&0xFF000000)) 
            {   
                // if the distance between high and low is small and there aren't
                // any bits we can roll off then force high and low to have common high 
                // order bits.
                if ((high-low < 0x10000))
                {
                    if (high-low > 0x1000)
                    {
                        high>>=1;
                        low>>=1;
                        high = low = high+low;
                        high += 0xFF;
                        low -= 0xFF;
                    } 
                    else /**/
                    {
                        high>>=1;
                        low>>=1;
                        high = low = high+low;
                    }
                }
                else
                {
                    // there are no bits to roll off and high and low are not
                    // too close so just quit the loop
                    break;
                }
                
            }  
            // else if there are 8 bits we can roll off
            else
            {
                // write the 8 high order bits from low into buf
                unsigned char buf = static_cast<unsigned char>(low>>24);


                // roll off the bits we just wrote to buf
                high <<= 8;  
                low <<= 8;               
                high |= 0xFF;  // note that it is ok to add 0xFF to high here because
                            // of the convention that high == real upper range - 1.
                            // so that means that if we want to shift the upper range
                            // left by one then we must shift a one into high also
                            // since real upper range == high + 0.999999999...

                // make sure low is never zero
                if (low == 0)
                    low = 1;

                // write buf to the output stream
                if (streambuf->sputn(reinterpret_cast<char*>(&buf),1)==0)
                {
                    throw std::ios_base::failure("error occurred in the entropy_encoder object");
                }                   
                
            } 

        } // while (true)

    }

// ----------------------------------------------------------------------------------------

    void entropy_encoder_kernel_2::
    flush (
    )
    {

        // flush low to the output stream


        unsigned char buf;


        buf = static_cast<unsigned char>((low >> 24)&0xFF);
        if (streambuf->sputn(reinterpret_cast<char*>(&buf),1) == 0)
            throw std::ios_base::failure("error occurred in the entropy_encoder object");




        buf = static_cast<unsigned char>((low >> 16)&0xFF);
        if (streambuf->sputn(reinterpret_cast<char*>(&buf),1)==0)
            throw std::ios_base::failure("error occurred in the entropy_encoder object");



        buf = static_cast<unsigned char>((low >> 8)&0xFF);
        if (streambuf->sputn(reinterpret_cast<char*>(&buf),1)==0)
            throw std::ios_base::failure("error occurred in the entropy_encoder object");


        buf = static_cast<unsigned char>((low)&0xFF);
        if (streambuf->sputn(reinterpret_cast<char*>(&buf),1)==0)
            throw std::ios_base::failure("error occurred in the entropy_encoder object");
        
    

        
        // make sure the stream buffer flushes to its I/O channel
        streambuf->pubsync();


        // reset the encoder state
        low = initial_low;
        high = initial_high;
    }

// ----------------------------------------------------------------------------------------

}
#endif // DLIB_ENTROPY_ENCODER_KERNEL_2_CPp_