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 "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;
 }
 }
 }