media/libtheora/lib/dec/bitwise.c

   1 /********************************************************************
   2  *                                                                  *
   3  * THIS FILE IS PART OF THE OggVorbis SOFTWARE CODEC SOURCE CODE.   *
   4  * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS     *
   5  * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
   6  * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.       *
   7  *                                                                  *
   8  * THE OggVorbis SOURCE CODE IS (C) COPYRIGHT 1994-2002             *
   9  * by the Xiph.Org Foundation http://www.xiph.org/                  *
  10  *                                                                  *
  11  ********************************************************************
  12
  13   function: packing variable sized words into an octet stream
  14   last mod: $Id: bitwise.c 14546 2008-02-29 01:14:05Z tterribe $
  15
  16  ********************************************************************/
  17
  18 /* We're 'MSb' endian; if we write a word but read individual bits,
  19    then we'll read the msb first */
  20
  21 #include <string.h>
  22 #include <stdlib.h>
  23 #include "bitwise.h"
  24
  25 void theorapackB_reset(oggpack_buffer *b){
  26   b->ptr=b->buffer;
  27   b->buffer[0]=0;
  28   b->endbit=b->endbyte=0;
  29 }
  30
  31 void theorapackB_readinit(oggpack_buffer *b,unsigned char *buf,int bytes){
  32   memset(b,0,sizeof(*b));
  33   b->buffer=b->ptr=buf;
  34   b->storage=bytes;
  35 }
  36
  37 int theorapackB_look1(oggpack_buffer *b,long *_ret){
  38   if(b->endbyte>=b->storage){
  39     *_ret=0L;
  40     return -1;
  41   }
  42   *_ret=((b->ptr[0]>>(7-b->endbit))&1);
  43   return 0;
  44 }
  45
  46 void theorapackB_adv1(oggpack_buffer *b){
  47   if(++(b->endbit)>7){
  48     b->endbit=0;
  49     b->ptr++;
  50     b->endbyte++;
  51   }
  52 }
  53
  54 /* bits <= 32 */
  55 int theorapackB_read(oggpack_buffer *b,int bits,long *_ret){
  56   long ret;
  57   long m;
  58   int fail;
  59   m=32-bits;
  60   bits+=b->endbit;
  61   if(b->endbyte+4>=b->storage){
  62     /* not the main path */
  63     if(b->endbyte*8+bits>b->storage*8){
  64       *_ret=0L;
  65       fail=-1;
  66       goto overflow;
  67     }
  68     /* special case to avoid reading b->ptr[0], which might be past the end of
  69         the buffer; also skips some useless accounting */
  70     else if(!bits){
  71       *_ret=0L;
  72       return 0;
  73     }
  74   }
  75   ret=b->ptr[0]<<(24+b->endbit);
  76   if(bits>8){
  77     ret|=b->ptr[1]<<(16+b->endbit);
  78     if(bits>16){
  79       ret|=b->ptr[2]<<(8+b->endbit);
  80       if(bits>24){
  81         ret|=b->ptr[3]<<(b->endbit);
  82         if(bits>32 && b->endbit)
  83           ret|=b->ptr[4]>>(8-b->endbit);
  84       }
  85     }
  86   }
  87   *_ret=((ret&0xffffffffUL)>>(m>>1))>>((m+1)>>1);
  88   fail=0;
  89 overflow:
  90   b->ptr+=bits/8;
  91   b->endbyte+=bits/8;
  92   b->endbit=bits&7;
  93   return fail;
  94 }
  95
  96 int theorapackB_read1(oggpack_buffer *b,long *_ret){
  97   int fail;
  98   if(b->endbyte>=b->storage){
  99     /* not the main path */
 100     *_ret=0L;
 101     fail=-1;
 102     goto overflow;
 103   }
 104   *_ret=(b->ptr[0]>>(7-b->endbit))&1;
 105   fail=0;
 106 overflow:
 107   b->endbit++;
 108   if(b->endbit>7){
 109     b->endbit=0;
 110     b->ptr++;
 111     b->endbyte++;
 112   }
 113   return fail;
 114 }
 115
 116 long theorapackB_bytes(oggpack_buffer *b){
 117   return(b->endbyte+(b->endbit+7)/8);
 118 }
 119
 120 long theorapackB_bits(oggpack_buffer *b){
 121   return(b->endbyte*8+b->endbit);
 122 }
 123
 124 unsigned char *theorapackB_get_buffer(oggpack_buffer *b){
 125   return(b->buffer);
 126 }