112 lines
3 KiB
C
112 lines
3 KiB
C
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/********************************************************************
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* *
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* THIS FILE IS PART OF THE OggTheora SOFTWARE CODEC SOURCE CODE. *
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* USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS *
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* GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
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* IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING. *
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* *
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* THE OggTheora SOURCE CODE IS (C) COPYRIGHT 1994-2009 *
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* by the Xiph.Org Foundation and contributors http://www.xiph.org/ *
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* *
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********************************************************************
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function: packing variable sized words into an octet stream
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last mod: $Id: bitpack.c 16503 2009-08-22 18:14:02Z giles $
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********************************************************************/
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#include <string.h>
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#include <stdlib.h>
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#include "bitpack.h"
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/*We're 'MSb' endian; if we write a word but read individual bits,
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then we'll read the MSb first.*/
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void oc_pack_readinit(oc_pack_buf *_b,unsigned char *_buf,long _bytes){
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memset(_b,0,sizeof(*_b));
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_b->ptr=_buf;
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_b->stop=_buf+_bytes;
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}
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static oc_pb_window oc_pack_refill(oc_pack_buf *_b,int _bits){
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const unsigned char *ptr;
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const unsigned char *stop;
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oc_pb_window window;
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int available;
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window=_b->window;
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available=_b->bits;
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ptr=_b->ptr;
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stop=_b->stop;
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while(available<=OC_PB_WINDOW_SIZE-8&&ptr<stop){
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available+=8;
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window|=(oc_pb_window)*ptr++<<OC_PB_WINDOW_SIZE-available;
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}
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_b->ptr=ptr;
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if(_bits>available){
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if(ptr>=stop){
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_b->eof=1;
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available=OC_LOTS_OF_BITS;
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}
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else window|=*ptr>>(available&7);
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}
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_b->bits=available;
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return window;
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}
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int oc_pack_look1(oc_pack_buf *_b){
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oc_pb_window window;
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int available;
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window=_b->window;
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available=_b->bits;
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if(available<1)_b->window=window=oc_pack_refill(_b,1);
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return window>>OC_PB_WINDOW_SIZE-1;
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}
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void oc_pack_adv1(oc_pack_buf *_b){
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_b->window<<=1;
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_b->bits--;
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}
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/*Here we assume that 0<=_bits&&_bits<=32.*/
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long oc_pack_read(oc_pack_buf *_b,int _bits){
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oc_pb_window window;
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int available;
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long result;
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window=_b->window;
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available=_b->bits;
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if(_bits==0)return 0;
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if(available<_bits){
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window=oc_pack_refill(_b,_bits);
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available=_b->bits;
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}
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result=window>>OC_PB_WINDOW_SIZE-_bits;
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available-=_bits;
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window<<=1;
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window<<=_bits-1;
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_b->bits=available;
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_b->window=window;
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return result;
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}
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int oc_pack_read1(oc_pack_buf *_b){
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oc_pb_window window;
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int available;
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int result;
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window=_b->window;
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available=_b->bits;
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if(available<1){
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window=oc_pack_refill(_b,1);
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available=_b->bits;
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}
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result=window>>OC_PB_WINDOW_SIZE-1;
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available--;
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window<<=1;
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_b->bits=available;
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_b->window=window;
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return result;
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}
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long oc_pack_bytes_left(oc_pack_buf *_b){
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if(_b->eof)return -1;
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return _b->stop-_b->ptr+(_b->bits>>3);
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}
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