freeswitch/libs/ilbc/src/packing.c

/*
 * iLBC - a library for the iLBC codec
 *
 * packing.c - The iLBC low bit rate speech codec.
 *
 * Adapted by Steve Underwood <steveu@coppice.org> from the reference
 * iLBC code supplied in RFC3951.
 *
 * Original code Copyright (C) The Internet Society (2004).
 * All changes to produce this version Copyright (C) 2008 by Steve Underwood
 * All Rights Reserved.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * $Id: packing.c,v 1.2 2008/03/06 12:27:38 steveu Exp $
 */

/*! \file */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

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

#include "ilbc.h"
#include "constants.h"
#include "helpfun.h"
#include "string.h"
#include "packing.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(uint8_t **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 |= (uint8_t) (index << (posLeft - bitno));
            *pos += bitno;
            bitno = 0;
        }
        else
        {
            **bitstream |= (uint8_t) (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(const uint8_t **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;
        }
    }
}