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/********************************************************************
* *
* THIS FILE IS PART OF THE OggTheora SOFTWARE CODEC SOURCE CODE. *
* USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS *
* GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
* IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING. *
* *
* THE OggTheora SOURCE CODE IS (C) COPYRIGHT 1994-2009 *
* by the Xiph.Org Foundation and contributors http://www.xiph.org/ *
* *
********************************************************************
function: packing variable sized words into an octet stream
last mod: $Id: bitpack.c 17410 2010-09-21 21:53:48Z tterribe $
********************************************************************/
#include <string.h>
#include <stdlib.h>
#include "bitpack.h"
/*We're 'MSb' endian; if we write a word but read individual bits,
then we'll read the MSb first.*/
void oc_pack_readinit(oc_pack_buf *_b,unsigned char *_buf,long _bytes){
memset(_b,0,sizeof(*_b));
_b->ptr=_buf;
_b->stop=_buf+_bytes;
}
static oc_pb_window oc_pack_refill(oc_pack_buf *_b,int _bits){
const unsigned char *ptr;
const unsigned char *stop;
oc_pb_window window;
int available;
unsigned shift;
stop=_b->stop;
ptr=_b->ptr;
window=_b->window;
available=_b->bits;
shift=OC_PB_WINDOW_SIZE-available;
while(7<shift&&ptr<stop){
shift-=8;
window|=(oc_pb_window)*ptr++<<shift;
}
_b->ptr=ptr;
available=OC_PB_WINDOW_SIZE-shift;
if(_bits>available){
if(ptr>=stop){
_b->eof=1;
available=OC_LOTS_OF_BITS;
}
else window|=*ptr>>(available&7);
}
_b->bits=available;
return window;
}
int oc_pack_look1(oc_pack_buf *_b){
oc_pb_window window;
int available;
window=_b->window;
available=_b->bits;
if(available<1)_b->window=window=oc_pack_refill(_b,1);
return window>>OC_PB_WINDOW_SIZE-1;
}
void oc_pack_adv1(oc_pack_buf *_b){
_b->window<<=1;
_b->bits--;
}
/*Here we assume that 0<=_bits&&_bits<=32.*/
long oc_pack_read_c(oc_pack_buf *_b,int _bits){
oc_pb_window window;
int available;
long result;
window=_b->window;
available=_b->bits;
if(_bits==0)return 0;
if(available<_bits){
window=oc_pack_refill(_b,_bits);
available=_b->bits;
}
result=window>>OC_PB_WINDOW_SIZE-_bits;
available-=_bits;
window<<=1;
window<<=_bits-1;
_b->window=window;
_b->bits=available;
return result;
}
int oc_pack_read1_c(oc_pack_buf *_b){
oc_pb_window window;
int available;
int result;
window=_b->window;
available=_b->bits;
if(available<1){
window=oc_pack_refill(_b,1);
available=_b->bits;
}
result=window>>OC_PB_WINDOW_SIZE-1;
available--;
window<<=1;
_b->window=window;
_b->bits=available;
return result;
}
long oc_pack_bytes_left(oc_pack_buf *_b){
if(_b->eof)return -1;
return _b->stop-_b->ptr+(_b->bits>>3);
}
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