libavcodec/rangecoder.c

   1 /*
   2  * Range coder
   3  * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
   4  *
   5  * This file is part of Libav.
   6  *
   7  * Libav 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  * Libav 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 Libav; 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 "avcodec.h"
  37 #include "rangecoder.h"
  38 #include "bytestream.h"
  39
  40 void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
  41 {
  42     c->bytestream_start  =
  43     c->bytestream        = buf;
  44     c->bytestream_end    = buf + buf_size;
  45     c->low               = 0;
  46     c->range             = 0xFF00;
  47     c->outstanding_count = 0;
  48     c->outstanding_byte  = -1;
  49 }
  50
  51 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size)
  52 {
  53     /* cast to avoid compiler warning */
  54     ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
  55
  56     c->low = bytestream_get_be16(&c->bytestream);
  57 }
  58
  59 void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
  60 {
  61     const int64_t one = 1LL << 32;
  62     int64_t p;
  63     int last_p8, p8, i;
  64
  65     memset(c->zero_state, 0, sizeof(c->zero_state));
  66     memset(c->one_state, 0, sizeof(c->one_state));
  67
  68     last_p8 = 0;
  69     p       = one / 2;
  70     for (i = 0; i < 128; i++) {
  71         p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
  72         if (p8 <= last_p8)
  73             p8 = last_p8 + 1;
  74         if (last_p8 && last_p8 < 256 && p8 <= max_p)
  75             c->one_state[last_p8] = p8;
  76
  77         p      += ((one - p) * factor + one / 2) >> 32;
  78         last_p8 = p8;
  79     }
  80
  81     for (i = 256 - max_p; i <= max_p; i++) {
  82         if (c->one_state[i])
  83             continue;
  84
  85         p  = (i * one + 128) >> 8;
  86         p += ((one - p) * factor + one / 2) >> 32;
  87         p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
  88         if (p8 <= i)
  89             p8 = i + 1;
  90         if (p8 > max_p)
  91             p8 = max_p;
  92         c->one_state[i] = p8;
  93     }
  94
  95     for (i = 1; i < 255; i++)
  96         c->zero_state[i] = 256 - c->one_state[256 - i];
  97 }
  98
  99 /* Return the number of bytes written. */
 100 int ff_rac_terminate(RangeCoder *c)
 101 {
 102     c->range = 0xFF;
 103     c->low  += 0xFF;
 104     renorm_encoder(c);
 105     c->range = 0xFF;
 106     renorm_encoder(c);
 107
 108     assert(c->low == 0);
 109     assert(c->range >= 0x100);
 110
 111     return c->bytestream - c->bytestream_start;
 112 }
 113
 114 #ifdef TEST
 115 #define SIZE 10240
 116
 117 #include "libavutil/lfg.h"
 118 #include "libavutil/log.h"
 119
 120 int main(void)
 121 {
 122     RangeCoder c;
 123     uint8_t b[9 * SIZE];
 124     uint8_t r[9 * SIZE];
 125     int i;
 126     uint8_t state[10];
 127     AVLFG prng;
 128
 129     av_lfg_init(&prng, 1);
 130
 131     ff_init_range_encoder(&c, b, SIZE);
 132     ff_build_rac_states(&c, 0.05 * (1LL << 32), 128 + 64 + 32 + 16);
 133
 134     memset(state, 128, sizeof(state));
 135
 136     for (i = 0; i < SIZE; i++)
 137         r[i] = av_lfg_get(&prng) % 7;
 138
 139     for (i = 0; i < SIZE; i++)
 140         put_rac(&c, state, r[i] & 1);
 141
 142     ff_rac_terminate(&c);
 143
 144     ff_init_range_decoder(&c, b, SIZE);
 145
 146     memset(state, 128, sizeof(state));
 147
 148     for (i = 0; i < SIZE; i++)
 149         if ((r[i] & 1) != get_rac(&c, state)) {
 150             av_log(NULL, AV_LOG_ERROR, "rac failure at %d\n", i);
 151             return 1;
 152         }
 153
 154     return 0;
 155 }
 156 #endif /* TEST */