ffmpeg/libavcodec/rangecoder.c

   1 /*
   2  * Range coder
   3  * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 /**
  23  * @file
  24  * Range coder.
  25  * based upon
  26  *    "Range encoding: an algorithm for removing redundancy from a digitised
  27  *                     message.
  28  *     G. N. N. Martin                  Presented in March 1979 to the Video &
  29  *                                      Data Recording Conference,
  30  *     IBM UK Scientific Center         held in Southampton July 24-27 1979."
  31  *
  32  */
  33
  34 #include <string.h>
  35
  36 #include "libavutil/attributes.h"
  37 #include "libavutil/avassert.h"
  38 #include "avcodec.h"
  39 #include "rangecoder.h"
  40 #include "bytestream.h"
  41
  42 av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
  43 {
  44     c->bytestream_start  =
  45     c->bytestream        = buf;
  46     c->bytestream_end    = buf + buf_size;
  47     c->low               = 0;
  48     c->range             = 0xFF00;
  49     c->outstanding_count = 0;
  50     c->outstanding_byte  = -1;
  51 }
  52
  53 av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf,
  54                                    int buf_size)
  55 {
  56     /* cast to avoid compiler warning */
  57     ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
  58
  59     c->low = bytestream_get_be16((const uint8_t **)&c->bytestream);
  60 }
  61
  62 void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
  63 {
  64     const int64_t one = 1LL << 32;
  65     int64_t p;
  66     int last_p8, p8, i;
  67
  68     memset(c->zero_state, 0, sizeof(c->zero_state));
  69     memset(c->one_state, 0, sizeof(c->one_state));
  70
  71     last_p8 = 0;
  72     p       = one / 2;
  73     for (i = 0; i < 128; i++) {
  74         p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
  75         if (p8 <= last_p8)
  76             p8 = last_p8 + 1;
  77         if (last_p8 && last_p8 < 256 && p8 <= max_p)
  78             c->one_state[last_p8] = p8;
  79
  80         p      += ((one - p) * factor + one / 2) >> 32;
  81         last_p8 = p8;
  82     }
  83
  84     for (i = 256 - max_p; i <= max_p; i++) {
  85         if (c->one_state[i])
  86             continue;
  87
  88         p  = (i * one + 128) >> 8;
  89         p += ((one - p) * factor + one / 2) >> 32;
  90         p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
  91         if (p8 <= i)
  92             p8 = i + 1;
  93         if (p8 > max_p)
  94             p8 = max_p;
  95         c->one_state[i] = p8;
  96     }
  97
  98     for (i = 1; i < 255; i++)
  99         c->zero_state[i] = 256 - c->one_state[256 - i];
 100 }
 101
 102 /* Return the number of bytes written. */
 103 int ff_rac_terminate(RangeCoder *c)
 104 {
 105     c->range = 0xFF;
 106     c->low  += 0xFF;
 107     renorm_encoder(c);
 108     c->range = 0xFF;
 109     renorm_encoder(c);
 110
 111     av_assert1(c->low   == 0);
 112     av_assert1(c->range >= 0x100);
 113
 114     return c->bytestream - c->bytestream_start;
 115 }
 116
 117 #ifdef TEST
 118 #define SIZE 10240
 119
 120 #include "libavutil/lfg.h"
 121 #include "libavutil/log.h"
 122
 123 static uint8_t b[9 * SIZE];
 124 static uint8_t r[9 * SIZE];
 125
 126 int main(void)
 127 {
 128     RangeCoder c;
 129     int i;
 130     uint8_t state[10];
 131     AVLFG prng;
 132
 133     av_lfg_init(&prng, 1);
 134
 135     ff_init_range_encoder(&c, b, SIZE);
 136     ff_build_rac_states(&c, 0.05 * (1LL << 32), 128 + 64 + 32 + 16);
 137
 138     memset(state, 128, sizeof(state));
 139
 140     for (i = 0; i < SIZE; i++)
 141         r[i] = av_lfg_get(&prng) % 7;
 142
 143     for (i = 0; i < SIZE; i++)
 144         put_rac(&c, state, r[i] & 1);
 145
 146     ff_rac_terminate(&c);
 147
 148     ff_init_range_decoder(&c, b, SIZE);
 149
 150     memset(state, 128, sizeof(state));
 151
 152     for (i = 0; i < SIZE; i++)
 153         if ((r[i] & 1) != get_rac(&c, state)) {
 154             av_log(NULL, AV_LOG_ERROR, "rac failure at %d\n", i);
 155             return 1;
 156         }
 157
 158     return 0;
 159 }
 160 #endif /* TEST */