quicktime/encore50/bitstream.c

   1
   2 /**************************************************************************
   3  *                                                                        *
   4  * This code is developed by Adam Li.  This software is an                *
   5  * implementation of a part of one or more MPEG-4 Video tools as          *
   6  * specified in ISO/IEC 14496-2 standard.  Those intending to use this    *
   7  * software module in hardware or software products are advised that its  *
   8  * use may infringe existing patents or copyrights, and any such use      *
   9  * would be at such party's own risk.  The original developer of this     *
  10  * software module and his/her company, and subsequent editors and their  *
  11  * companies (including Project Mayo), will have no liability for use of  *
  12  * this software or modifications or derivatives thereof.                 *
  13  *                                                                        *
  14  * Project Mayo gives users of the Codec a license to this software       *
  15  * module or modifications thereof for use in hardware or software        *
  16  * products claiming conformance to the MPEG-4 Video Standard as          *
  17  * described in the Open DivX license.                                    *
  18  *                                                                        *
  19  * The complete Open DivX license can be found at                         *
  20  * http://www.projectmayo.com/opendivx/license.php .                      *
  21  *                                                                        *
  22  **************************************************************************/
  23
  24 /**************************************************************************
  25  *
  26  *  mom_bitstream.c
  27  *
  28  *  Copyright (C) 2001  Project Mayo
  29  *
  30  *  Adam Li
  31  *
  32  *  DivX Advance Research Center <darc@projectmayo.com>
  33  *
  34  **************************************************************************/
  35
  36 #include "bitstream.h"
  37
  38 /* to mask the n least significant bits of an integer */
  39
  40 static unsigned int mask[33] =
  41 {
  42   0x00000000, 0x00000001, 0x00000003, 0x00000007,
  43   0x0000000f, 0x0000001f, 0x0000003f, 0x0000007f,
  44   0x000000ff, 0x000001ff, 0x000003ff, 0x000007ff,
  45   0x00000fff, 0x00001fff, 0x00003fff, 0x00007fff,
  46   0x0000ffff, 0x0001ffff, 0x0003ffff, 0x0007ffff,
  47   0x000fffff, 0x001fffff, 0x003fffff, 0x007fffff,
  48   0x00ffffff, 0x01ffffff, 0x03ffffff, 0x07ffffff,
  49   0x0fffffff, 0x1fffffff, 0x3fffffff, 0x7fffffff,
  50   0xffffffff
  51 };
  52
  53
  54 /* static data for pointers and counters */
  55
  56 /* byte pointer to the output bitstream */
  57 static unsigned char *byteptr;
  58 /* counter of how many bytes got written to the bitstream */
  59 static int bytecnt;
  60
  61 /* a one byte temporary buffer */
  62 static unsigned char outbfr;
  63 /* counter of how many unused bits left in the byte buffer */
  64 static int outcnt;
  65
  66 void Bitstream_Init(void *buffer)
  67 {
  68         byteptr = (unsigned char *)buffer;
  69         bytecnt = 0;
  70         outbfr = 0;
  71         outcnt = 8;
  72 }
  73
  74 void Bitstream_PutBits(int n, unsigned int val)
  75 {
  76         int diff;
  77 //printf("Bitstream_PutBits %d %02x\n", n, val);
  78
  79         while ((diff = n - outcnt) >= 0) { /* input is longer than what is left in the buffer */
  80                 outbfr |= (unsigned char)(val >> diff);
  81                 /* note that the first byte of the integer is the least significant byte */
  82                 n = diff;
  83                 val &= mask[n];
  84
  85                 *(byteptr ++) = outbfr;
  86                 bytecnt++;
  87                 outbfr = 0;
  88                 outcnt = 8;
  89         }
  90
  91         if (n > 0) { /* input is short enough to fit in what is left in the buffer */
  92                 outbfr |= (unsigned char)(val << (-diff));
  93                 outcnt -= n;
  94         }
  95 }
  96
  97
  98 int Bitstream_Close()
  99 {
 100         while (outcnt != 8) Bitstream_PutBits(1, 1);
 101         return bytecnt;
 102 }
 103
 104
 105 int Bitstream_NextStartCode()
 106 {
 107         int count = outcnt;
 108
 109         Bitstream_PutBits(1,0);
 110         while (outcnt != 8) Bitstream_PutBits(1, 1);
 111
 112         return (count);
 113 }
 114
 115
 116 int Bitstream_GetLength()
 117 {
 118         return bytecnt;
 119 }
 120
 121