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godotengine
GitHub Repository: godotengine/godot
 Path: blob/master/thirdparty/libtheora/bitpack.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                      *

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 * https://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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 ********************************************************************/

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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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  unsigned             shift;

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  stop=_b->stop;

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  ptr=_b->ptr;

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  window=_b->window;

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  available=_b->bits;

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  shift=OC_PB_WINDOW_SIZE-available;

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  while(7<shift&&ptr<stop){

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    shift-=8;

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    window|=(oc_pb_window)*ptr++<<shift;

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  }

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  _b->ptr=ptr;

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  available=OC_PB_WINDOW_SIZE-shift;

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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_c(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->window=window;

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  _b->bits=available;

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  return result;

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}

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int oc_pack_read1_c(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->window=window;

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  _b->bits=available;

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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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