biaridecod.c

Mobile IP VCEG的信道模拟程序

/***************************************************************************
 *
 * Module      :  biaridecod.c
 *
 * Authors:    :  Detlev Marpe 
 *				  Gabi Bl鋞termann
 *
 * Date        :  21. Oct 2000
 *
 * Description :  binary arithmetic
 *                decoder routines 
 *                
 *      Copyright (C) 2000 HEINRICH HERTZ INSTITUTE All Rights Reserved.
 *
 **************************************************************************
 */

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include "global.h"
#include "biaridecod.h"

extern int symbolCount;
/************************************************************************
 * M a c r o s
 ***********************************************************************
 */

#define get_byte(){                                                     \
						Dbuffer = Dcodestrm[(*Dcodestrm_len)++];        \
                        Dbits_to_go = 7;                                \
				  }


/************************************************************************/
/************************************************************************/
                    /* init / exit decoder */
/************************************************************************/
/************************************************************************/


/************************************************************************
 * arideco_create_decoding_environment():
 *
 * return: DecodingContextPtr
 ***********************************************************************
 */

DecodingEnvironmentPtr arideco_create_decoding_environment()
{
    DecodingEnvironmentPtr dep;

    if ((dep = calloc(1,sizeof(DecodingEnvironment))) == NULL)
        no_mem_exit(1);
    return dep;
}


/************************************************************************
 * arideco_delete_decoding_environment():
 *
 * return: void
 ***********************************************************************
 */

void arideco_delete_decoding_environment(DecodingEnvironmentPtr dep)
{
    if (dep == NULL)
        no_mem_exit(1);
    else
        free(dep);
}


/************************************************************************
 * arideco_start_decoding():
 *
 * return: void
 ***********************************************************************
 */
void arideco_start_decoding(DecodingEnvironmentPtr dep, unsigned char *cpixcode,
                            int firstbyte, int *cpixcode_len )
{
    int i;
    int bits;

    bits = CODE_VALUE_BITS;

    Dcodestrm = cpixcode;
    Dcodestrm_len = cpixcode_len;
    *Dcodestrm_len = firstbyte;

    Dbits_to_go = 0;
    dep->Dvalue = 0;

    for (i = 0; i < bits; i++) 
    {
        if (--Dbits_to_go < 0) 
	        get_byte();
        dep->Dvalue += dep->Dvalue  + (Dbuffer & 1);
        Dbuffer >>= 1;           
    }
    dep->Dlow = 0;
    dep->Dhigh = TOP_VALUE;
}  


/************************************************************************
 * arideco_bits_read():
 *
 * return: void
 ***********************************************************************
 */

int arideco_bits_read(DecodingEnvironmentPtr dep)
{
    return 8 * ((*Dcodestrm_len)-1) + (8 - Dbits_to_go) - CODE_VALUE_BITS;
}


/************************************************************************
 * arideco_done_decoding():
 *
 * return: void
 ***********************************************************************
 */
void arideco_done_decoding(DecodingEnvironmentPtr dep)
{
    (*Dcodestrm_len)++;
}   



/************************************************************************
 * biari_decode_symbol():
 *
 *
 * return: the decoded symbol
 ***********************************************************************
 */
unsigned int biari_decode_symbol(DecodingEnvironmentPtr dep, BiContextTypePtr bi_ct )
{
    unsigned int scaled_range;
    unsigned int symbol=0;
	int Dlow_m1 = dep->Dlow - 1;

#if  AAC_FRAC_TABLE
    if ( (scaled_range =  ( ( (dep->Dhigh - Dlow_m1) * ((bi_ct->cum_freq[1]*ARITH_CUM_FREQ_TABLE[bi_ct->cum_freq[0]])>>16))>>10) ) >=  (dep->Dvalue - Dlow_m1) )
#else
 	if ( (scaled_range =  ( ( (dep->Dhigh - Dlow_m1) * bi_ct->cum_freq[1]) / bi_ct->cum_freq[0] )) >=  (dep->Dvalue - Dlow_m1) )
#endif			
	{
        symbol++;
		dep->Dhigh = Dlow_m1 + scaled_range;
		bi_ct->cum_freq[1]++;
	}
	else
		dep->Dlow += scaled_range;

	if (++bi_ct->cum_freq[0] >= bi_ct->max_cum_freq) 
		rescale_cum_freq(bi_ct);

    do
	{
        if (dep->Dhigh >= HALF) 
		{
            if (dep->Dlow < HALF)
                if (dep->Dlow >= FIRST_QTR && dep->Dhigh < THIRD_QTR) 
				{
                    dep->Dhigh -= FIRST_QTR;   
					dep->Dvalue -= FIRST_QTR;                          
					dep->Dlow -= FIRST_QTR;
                } 
			    else
                    break;
            else 
			{
                dep->Dhigh -= HALF;
				dep->Dvalue -= HALF;
                dep->Dlow -= HALF;                  
            }
        }
        dep->Dlow <<= 1;
		dep->Dhigh += dep->Dhigh+1;

        if (--Dbits_to_go < 0) 
	        get_byte();

        dep->Dvalue += dep->Dvalue  + (Dbuffer & 1);
        Dbuffer >>= 1;           
    }
    while (1);

//    fprintf(p_trace,"@%d  %4.x  %4.x\n",symbolCount,Dlow,Dhigh);
       
    return symbol;
}   



/************************************************************************
*
*  Name :		biari_init_context()
*
*  Description: Initializes a given context with some pre-defined probabilities 
*				and a maximum symbol count for triggering the rescaling 
*
************************************************************************/
void biari_init_context( BiContextTypePtr ctx, int ini_count_0, int ini_count_1, int max_cum_freq )
{
	  
	ctx->in_use       = TRUE;
	ctx->max_cum_freq = max_cum_freq;
		
		
	ctx->cum_freq[1]  = ini_count_1;
	ctx->cum_freq[0]  = ini_count_0 + ini_count_1;
	
}  


/************************************************************************
 * biari_copy_context():
 *
 *
 * return:
 *      void
 ***********************************************************************
 */
void biari_copy_context( BiContextTypePtr ctx_orig, BiContextTypePtr ctx_dest )
{

    ctx_dest->in_use     =  ctx_orig->in_use;
	ctx_dest->max_cum_freq = ctx_orig->max_cum_freq;

    ctx_dest->cum_freq[1] = ctx_orig->cum_freq[1];
    ctx_dest->cum_freq[0] = ctx_orig->cum_freq[0];

    return;

}   

/************************************************************************
 * biari_print_context():
 *
 * return:
 *      void
 ***********************************************************************
 */
void biari_print_context( BiContextTypePtr ctx )
{

    printf("0: %4d\t",ctx->cum_freq[0] - ctx->cum_freq[1]);
    printf("1: %4d",ctx->cum_freq[1]);
	
	return;

}  
 

 /************************************************************************
*
*  Name :		rescale_cum_freq()
*
*  Description: Rescales a given context model by halvening the symbol counts
*
************************************************************************/
void rescale_cum_freq( BiContextTypePtr   bi_ct)
{

	int old_cum_freq_of_one = bi_ct->cum_freq[1];

    bi_ct->cum_freq[1] = (bi_ct->cum_freq[1] + 1) >> 1;
    bi_ct->cum_freq[0] = bi_ct->cum_freq[1] + 
						( ( bi_ct->cum_freq[0] - old_cum_freq_of_one + 1 ) >> 1);
}