packing.c

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/******************************************************************

    iLBC Speech Coder ANSI-C Source Code

    packing.c 

    Copyright (C) The Internet Society (2004). 
    All Rights Reserved.

******************************************************************/

#include <math.h>
#include <stdlib.h>

#include "iLBC_define.h"
#include "constants.h"
#include "helpfun.h"
#include "packing.h"
#include "string.h"

/*----------------------------------------------------------------*
 *  splitting an integer into first most significant bits and 
 *  remaining least significant bits
 *---------------------------------------------------------------*/

void packsplit(
    int *index,                 /* (i) the value to split */
    int *firstpart,             /* (o) the value specified by most 
                                       significant bits */
    int *rest,                  /* (o) the value specified by least
                                       significant bits */
    int bitno_firstpart,    /* (i) number of bits in most 
                                       significant part */
    int bitno_total             /* (i) number of bits in full range
                                       of value */
){
    int bitno_rest = bitno_total-bitno_firstpart;



    *firstpart = *index>>(bitno_rest);
    *rest = *index-(*firstpart<<(bitno_rest));
}

/*----------------------------------------------------------------*
 *  combining a value corresponding to msb's with a value 
 *  corresponding to lsb's
 *---------------------------------------------------------------*/

void packcombine( 
    int *index,                 /* (i/o) the msb value in the 
                                       combined value out */
    int rest,                   /* (i) the lsb value */
    int bitno_rest              /* (i) the number of bits in the 
                                       lsb part */
){
    *index = *index<<bitno_rest;
    *index += rest;
}

/*----------------------------------------------------------------*
 *  packing of bits into bitstream, i.e., vector of bytes
 *---------------------------------------------------------------*/

void dopack( 
    unsigned char **bitstream,  /* (i/o) on entrance pointer to 
                                       place in bitstream to pack 
                                       new data, on exit pointer 
                                       to place in bitstream to 
                                       pack future data */
    int index,                  /* (i) the value to pack */
    int bitno,                  /* (i) the number of bits that the 
                                       value will fit within */
    int *pos                /* (i/o) write position in the 
                                       current byte */
){
    int posLeft;
    
    /* Clear the bits before starting in a new byte */
    
    if ((*pos)==0) {
        **bitstream=0;
    }

    while (bitno>0) {
        
        /* Jump to the next byte if end of this byte is reached*/
        
        if (*pos==8) {
            *pos=0;
            (*bitstream)++;
            **bitstream=0;
        }



        posLeft=8-(*pos);

        /* Insert index into the bitstream */
        
        if (bitno <= posLeft) {
            **bitstream |= (unsigned char)(index<<(posLeft-bitno));
            *pos+=bitno;
            bitno=0;
        } else {
            **bitstream |= (unsigned char)(index>>(bitno-posLeft));
            
            *pos=8;
            index-=((index>>(bitno-posLeft))<<(bitno-posLeft));
            
            bitno-=posLeft;
        }
    }
}

/*----------------------------------------------------------------*
 *  unpacking of bits from bitstream, i.e., vector of bytes
 *---------------------------------------------------------------*/

void unpack( 
    unsigned char **bitstream,  /* (i/o) on entrance pointer to 
                                       place in bitstream to 
                                       unpack new data from, on 
                                       exit pointer to place in 
                                       bitstream to unpack future 
                                       data from */
    int *index,                 /* (o) resulting value */
    int bitno,                  /* (i) number of bits used to 
                                       represent the value */
    int *pos                /* (i/o) read position in the 
                                       current byte */
){
    int BitsLeft;

    *index=0;

    while (bitno>0) {
        
        /* move forward in bitstream when the end of the 
           byte is reached */
        
        if (*pos==8) {
            *pos=0;
            (*bitstream)++;
        }

        BitsLeft=8-(*pos);

        /* Extract bits to index */
        


        if (BitsLeft>=bitno) {
            *index+=((((**bitstream)<<(*pos)) & 0xFF)>>(8-bitno));
            
            *pos+=bitno;
            bitno=0;
        } else {
            
            if ((8-bitno)>0) {
                *index+=((((**bitstream)<<(*pos)) & 0xFF)>>
                    (8-bitno));
                *pos=8;
            } else {
                *index+=(((int)(((**bitstream)<<(*pos)) & 0xFF))<<
                    (bitno-8));
                *pos=8;
            }
            bitno-=BitsLeft;
        }
    }
}