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 /**
  24  * @file rangecoder.c
  25  * Range coder.
  26  * based upon
  27  *    "Range encoding: an algorithm for removing redundancy from a digitised
  28  *                     message.
  29  *     G. N. N. Martin                  Presented in March 1979 to the Video &
  30  *                                      Data Recording Conference,
  31  *     IBM UK Scientific Center         held in Southampton July 24-27 1979."
  32  *
  33  */
  34
  35 #include <string.h>
  36
  37 #include "avcodec.h"
  38 #include "rangecoder.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 =(*c->bytestream++)<<8;
  57     c->low+= *c->bytestream++;
  58 }
  59
  60 void ff_build_rac_states(RangeCoder *c, int factor, int max_p){
  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) p8= last_p8+1;
  73         if(last_p8 && last_p8<256 && p8<=max_p)
  74             c->one_state[last_p8]= p8;
  75
  76         p+= ((one-p)*factor + one/2) >> 32;
  77         last_p8= p8;
  78     }
  79
  80     for(i=256-max_p; i<=max_p; i++){
  81         if(c->one_state[i])
  82             continue;
  83
  84         p= (i*one + 128) >> 8;
  85         p+= ((one-p)*factor + one/2) >> 32;
  86         p8= (256*p + one/2) >> 32; //FIXME try without the one
  87         if(p8 <= i) p8= i+1;
  88         if(p8 > max_p) p8= max_p;
  89         c->one_state[    i]=     p8;
  90     }
  91
  92     for(i=1; i<255; i++)
  93         c->zero_state[i]= 256-c->one_state[256-i];
  94 }
  95
  96 /**
  97  *
  98  * @return the number of bytes written
  99  */
 100 int ff_rac_terminate(RangeCoder *c){
 101     c->range=0xFF;
 102     c->low +=0xFF;
 103     renorm_encoder(c);
 104     c->range=0xFF;
 105     renorm_encoder(c);
 106
 107     assert(c->low   == 0);
 108     assert(c->range >= 0x100);
 109
 110     return c->bytestream - c->bytestream_start;
 111 }
 112
 113 #if 0 //selftest
 114 #define SIZE 10240
 115 int main(){
 116     RangeCoder c;
 117     uint8_t b[9*SIZE];
 118     uint8_t r[9*SIZE];
 119     int i;
 120     uint8_t state[10]= {0};
 121
 122     ff_init_range_encoder(&c, b, SIZE);
 123     ff_build_rac_states(&c, 0.05*(1LL<<32), 128+64+32+16);
 124
 125     memset(state, 128, sizeof(state));
 126
 127     for(i=0; i<SIZE; i++){
 128         r[i]= random()%7;
 129     }
 130
 131     for(i=0; i<SIZE; i++){
 132 START_TIMER
 133         put_rac(&c, state, r[i]&1);
 134 STOP_TIMER("put_rac")
 135     }
 136
 137     ff_put_rac_terminate(&c);
 138
 139     ff_init_range_decoder(&c, b, SIZE);
 140
 141     memset(state, 128, sizeof(state));
 142
 143     for(i=0; i<SIZE; i++){
 144 START_TIMER
 145         if( (r[i]&1) != get_rac(&c, state) )
 146             av_log(NULL, AV_LOG_DEBUG, "rac failure at %d\n", i);
 147 STOP_TIMER("get_rac")
 148     }
 149
 150     return 0;
 151 }
 152 #endif