src/gallium/auxiliary/vl/vl_bitstream_parser.c

   1 /**************************************************************************
   2  *
   3  * Copyright 2009 Younes Manton.
   4  * All Rights Reserved.
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a
   7  * copy of this software and associated documentation files (the
   8  * "Software"), to deal in the Software without restriction, including
   9  * without limitation the rights to use, copy, modify, merge, publish,
  10  * distribute, sub license, and/or sell copies of the Software, and to
  11  * permit persons to whom the Software is furnished to do so, subject to
  12  * the following conditions:
  13  *
  14  * The above copyright notice and this permission notice (including the
  15  * next paragraph) shall be included in all copies or substantial portions
  16  * of the Software.
  17  *
  18  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  19  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  20  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
  21  * IN NO EVENT SHALL TUNGSTEN GRAPHICS AND/OR ITS SUPPLIERS BE LIABLE FOR
  22  * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  23  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  24  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  25  *
  26  **************************************************************************/
  27
  28 #include "vl_bitstream_parser.h"
  29 #include <assert.h>
  30 #include <limits.h>
  31 #include <util/u_memory.h>
  32
  33 static unsigned
  34 grab_bits(unsigned cursor, unsigned how_many_bits, unsigned bitstream_elt)
  35 {
  36    unsigned excess_bits = sizeof(unsigned) * CHAR_BIT - how_many_bits - cursor;
  37
  38    assert(cursor < sizeof(unsigned) * CHAR_BIT);
  39    assert(how_many_bits > 0 && how_many_bits <= sizeof(unsigned) * CHAR_BIT);
  40    assert(cursor + how_many_bits <= sizeof(unsigned) * CHAR_BIT);
  41
  42    return (bitstream_elt << excess_bits) >> (excess_bits + cursor);
  43 }
  44
  45 static unsigned
  46 show_bits(unsigned cursor, unsigned how_many_bits, const unsigned *bitstream)
  47 {
  48    unsigned cur_int = cursor / (sizeof(unsigned) * CHAR_BIT);
  49    unsigned cur_bit = cursor % (sizeof(unsigned) * CHAR_BIT);
  50
  51    assert(bitstream);
  52
  53    if (cur_bit + how_many_bits > sizeof(unsigned) * CHAR_BIT) {
  54       unsigned lower = grab_bits(cur_bit, sizeof(unsigned) * CHAR_BIT - cur_bit,
  55                                  bitstream[cur_int]);
  56       unsigned upper = grab_bits(0, cur_bit + how_many_bits - sizeof(unsigned) * CHAR_BIT,
  57                                  bitstream[cur_int + 1]);
  58       return lower | upper << (sizeof(unsigned) * CHAR_BIT - cur_bit);
  59    }
  60    else
  61       return grab_bits(cur_bit, how_many_bits, bitstream[cur_int]);
  62 }
  63
  64 bool vl_bitstream_parser_init(struct vl_bitstream_parser *parser,
  65                               unsigned num_bitstreams,
  66                               const void **bitstreams,
  67                               const unsigned *sizes)
  68 {
  69    assert(parser);
  70    assert(num_bitstreams);
  71    assert(bitstreams);
  72    assert(sizes);
  73
  74    parser->num_bitstreams = num_bitstreams;
  75    parser->bitstreams = (const unsigned**)bitstreams;
  76    parser->sizes = sizes;
  77    parser->cur_bitstream = 0;
  78    parser->cursor = 0;
  79
  80    return true;
  81 }
  82
  83 void vl_bitstream_parser_cleanup(struct vl_bitstream_parser *parser)
  84 {
  85    assert(parser);
  86 }
  87
  88 unsigned
  89 vl_bitstream_parser_get_bits(struct vl_bitstream_parser *parser,
  90                              unsigned how_many_bits)
  91 {
  92    unsigned bits;
  93
  94    assert(parser);
  95
  96    bits = vl_bitstream_parser_show_bits(parser, how_many_bits);
  97
  98    vl_bitstream_parser_forward(parser, how_many_bits);
  99
 100    return bits;
 101 }
 102
 103 unsigned
 104 vl_bitstream_parser_show_bits(struct vl_bitstream_parser *parser,
 105                               unsigned how_many_bits)
 106 {
 107    unsigned bits = 0;
 108    unsigned shift = 0;
 109    unsigned cursor;
 110    unsigned cur_bitstream;
 111
 112    assert(parser);
 113
 114    cursor = parser->cursor;
 115    cur_bitstream = parser->cur_bitstream;
 116
 117    while (1) {
 118       unsigned bits_left = parser->sizes[cur_bitstream] * CHAR_BIT - cursor;
 119       unsigned bits_to_show = how_many_bits > bits_left ? bits_left : how_many_bits;
 120
 121       bits |= show_bits(cursor, bits_to_show,
 122                         parser->bitstreams[cur_bitstream]) << shift;
 123
 124       if (how_many_bits > bits_to_show) {
 125          how_many_bits -= bits_to_show;
 126          cursor = 0;
 127          ++cur_bitstream;
 128          shift += bits_to_show;
 129       }
 130       else
 131          break;
 132    }
 133
 134    return bits;
 135 }
 136
 137 void vl_bitstream_parser_forward(struct vl_bitstream_parser *parser,
 138                                  unsigned how_many_bits)
 139 {
 140    assert(parser);
 141    assert(how_many_bits);
 142
 143    parser->cursor += how_many_bits;
 144
 145    while (parser->cursor > parser->sizes[parser->cur_bitstream] * CHAR_BIT) {
 146       parser->cursor -= parser->sizes[parser->cur_bitstream++] * CHAR_BIT;
 147       assert(parser->cur_bitstream < parser->num_bitstreams);
 148    }
 149 }
 150
 151 void vl_bitstream_parser_rewind(struct vl_bitstream_parser *parser,
 152                                 unsigned how_many_bits)
 153 {
 154    signed c;
 155
 156    assert(parser);
 157    assert(how_many_bits);
 158
 159    c = parser->cursor - how_many_bits;
 160
 161    while (c < 0) {
 162       c += parser->sizes[parser->cur_bitstream--] * CHAR_BIT;
 163       assert(parser->cur_bitstream < parser->num_bitstreams);
 164    }
 165
 166    parser->cursor = (unsigned)c;
 167 }