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 41void 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 52void 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 59void 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 */ 99int 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 117int 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++){ 137START_TIMER 138 put_rac(&c, state, r[i]&1); 139STOP_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++){ 149START_TIMER 150 if( (r[i]&1) != get_rac(&c, state) ) 151 av_log(NULL, AV_LOG_DEBUG, "rac failure at %d\n", i); 152STOP_TIMER("get_rac") 153 } 154 155 return 0; 156} 157#endif /* TEST */ 158