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 libavcodec/rangecoder.c
  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
  41 void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size){
  42     c->bytestream_start=
  43     c->bytestream= buf;
  44     c->bytestream_end= buf + buf_size;
  45
  46     c->low= 0;
  47     c->range= 0xFF00;
  48     c->outstanding_count= 0;
  49     c->outstanding_byte= -1;
  50 }
  51
  52 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size){
  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     const int64_t one= 1LL<<32;
  61     int64_t p;
  62     int last_p8, p8, i;
  63
  64     memset(c->zero_state, 0, sizeof(c->zero_state));
  65     memset(c-> one_state, 0, sizeof(c-> one_state));
  66
  67     last_p8= 0;
  68     p= one/2;
  69     for(i=0; i<128; i++){
  70         p8= (256*p + one/2) >> 32; //FIXME try without the one
  71         if(p8 <= last_p8) p8= last_p8+1;
  72         if(last_p8 && last_p8<256 && p8<=max_p)
  73             c->one_state[last_p8]= p8;
  74
  75         p+= ((one-p)*factor + one/2) >> 32;
  76         last_p8= p8;
  77     }
  78
  79     for(i=256-max_p; i<=max_p; i++){
  80         if(c->one_state[i])
  81             continue;
  82
  83         p= (i*one + 128) >> 8;
  84         p+= ((one-p)*factor + one/2) >> 32;
  85         p8= (256*p + one/2) >> 32; //FIXME try without the one
  86         if(p8 <= i) p8= i+1;
  87         if(p8 > max_p) p8= max_p;
  88         c->one_state[    i]=     p8;
  89     }
  90
  91     for(i=1; i<255; i++)
  92         c->zero_state[i]= 256-c->one_state[256-i];
  93 }
  94
  95 /**
  96  *
  97  * @return the number of bytes written
  98  */
  99 int ff_rac_terminate(RangeCoder *c){
 100     c->range=0xFF;
 101     c->low +=0xFF;
 102     renorm_encoder(c);
 103     c->range=0xFF;
 104     renorm_encoder(c);
 105
 106     assert(c->low   == 0);
 107     assert(c->range >= 0x100);
 108
 109     return c->bytestream - c->bytestream_start;
 110 }
 111
 112 #ifdef TEST
 113 #define SIZE 10240
 114
 115 #include "libavutil/lfg.h"
 116
 117 int main(void){
 118     RangeCoder c;
 119     uint8_t b[9*SIZE];
 120     uint8_t r[9*SIZE];
 121     int i;
 122     uint8_t state[10]= {0};
 123     AVLFG prng;
 124
 125     av_lfg_init(&prng, 1);
 126
 127     ff_init_range_encoder(&c, b, SIZE);
 128     ff_build_rac_states(&c, 0.05*(1LL<<32), 128+64+32+16);
 129
 130     memset(state, 128, sizeof(state));
 131
 132     for(i=0; i<SIZE; i++){
 133         r[i] = av_lfg_get(&prng) % 7;
 134     }
 135
 136     for(i=0; i<SIZE; i++){
 137 START_TIMER
 138         put_rac(&c, state, r[i]&1);
 139 STOP_TIMER("put_rac")
 140     }
 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 START_TIMER
 150         if( (r[i]&1) != get_rac(&c, state) )
 151             av_log(NULL, AV_LOG_DEBUG, "rac failure at %d\n", i);
 152 STOP_TIMER("get_rac")
 153     }
 154
 155     return 0;
 156 }
 157 #endif /* TEST */