The Tor Browser: media/libtheora/lib/bitpack.c@b8a032363ba2

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

     1 /********************************************************************

     2  *                                                                  *

     3  * THIS FILE IS PART OF THE OggTheora 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 OggTheora SOURCE CODE IS (C) COPYRIGHT 1994-2009             *

     9  * by the Xiph.Org Foundation and contributors http://www.xiph.org/ *

    10  *                                                                  *

    11  ********************************************************************

    13   function: packing variable sized words into an octet stream

    14   last mod: $Id: bitpack.c 17410 2010-09-21 21:53:48Z tterribe $

    16  ********************************************************************/

    17 #include <string.h>

    18 #include <stdlib.h>

    19 #include "bitpack.h"

    21 /*We're 'MSb' endian; if we write a word but read individual bits,

    22    then we'll read the MSb first.*/

    24 void oc_pack_readinit(oc_pack_buf *_b,unsigned char *_buf,long _bytes){

    25   memset(_b,0,sizeof(*_b));

    26   _b->ptr=_buf;

    27   _b->stop=_buf+_bytes;

    28 }

    30 static oc_pb_window oc_pack_refill(oc_pack_buf *_b,int _bits){

    31   const unsigned char *ptr;

    32   const unsigned char *stop;

    33   oc_pb_window         window;

    34   int                  available;

    35   unsigned             shift;

    36   stop=_b->stop;

    37   ptr=_b->ptr;

    38   window=_b->window;

    39   available=_b->bits;

    40   shift=OC_PB_WINDOW_SIZE-available;

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

    42     shift-=8;

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

    44   }

    45   _b->ptr=ptr;

    46   available=OC_PB_WINDOW_SIZE-shift;

    47   if(_bits>available){

    48     if(ptr>=stop){

    49       _b->eof=1;

    50       available=OC_LOTS_OF_BITS;

    51     }

    52     else window|=*ptr>>(available&7);

    53   }

    54   _b->bits=available;

    55   return window;

    56 }

    58 int oc_pack_look1(oc_pack_buf *_b){

    59   oc_pb_window window;

    60   int          available;

    61   window=_b->window;

    62   available=_b->bits;

    63   if(available<1)_b->window=window=oc_pack_refill(_b,1);

    64   return window>>OC_PB_WINDOW_SIZE-1;

    65 }

    67 void oc_pack_adv1(oc_pack_buf *_b){

    68   _b->window<<=1;

    69   _b->bits--;

    70 }

    72 /*Here we assume that 0<=_bits&&_bits<=32.*/

    73 long oc_pack_read_c(oc_pack_buf *_b,int _bits){

    74   oc_pb_window window;

    75   int          available;

    76   long         result;

    77   window=_b->window;

    78   available=_b->bits;

    79   if(_bits==0)return 0;

    80   if(available<_bits){

    81     window=oc_pack_refill(_b,_bits);

    82     available=_b->bits;

    83   }

    84   result=window>>OC_PB_WINDOW_SIZE-_bits;

    85   available-=_bits;

    86   window<<=1;

    87   window<<=_bits-1;

    88   _b->window=window;

    89   _b->bits=available;

    90   return result;

    91 }

    93 int oc_pack_read1_c(oc_pack_buf *_b){

    94   oc_pb_window window;

    95   int          available;

    96   int          result;

    97   window=_b->window;

    98   available=_b->bits;

    99   if(available<1){

   100     window=oc_pack_refill(_b,1);

   101     available=_b->bits;

   102   }

   103   result=window>>OC_PB_WINDOW_SIZE-1;

   104   available--;

   105   window<<=1;

   106   _b->window=window;

   107   _b->bits=available;

   108   return result;

   109 }

   111 long oc_pack_bytes_left(oc_pack_buf *_b){

   112   if(_b->eof)return -1;

   113   return _b->stop-_b->ptr+(_b->bits>>3);

   114 }

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