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/*
* Range coder
* Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
*
* This file is part of Libav.
*
* Libav is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* Libav is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with Libav; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file
* Range coder.
* based upon
* "Range encoding: an algorithm for removing redundancy from a digitised
* message.
* G. N. N. Martin Presented in March 1979 to the Video &
* Data Recording Conference,
* IBM UK Scientific Center held in Southampton July 24-27 1979."
*
*/
#include <string.h>
#include "avcodec.h"
#include "rangecoder.h"
#include "bytestream.h"
void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size){
c->bytestream_start=
c->bytestream= buf;
c->bytestream_end= buf + buf_size;
c->low= 0;
c->range= 0xFF00;
c->outstanding_count= 0;
c->outstanding_byte= -1;
}
void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size){
/* cast to avoid compiler warning */
ff_init_range_encoder(c, (uint8_t *) buf, buf_size);
c->low = bytestream_get_be16(&c->bytestream);
}
void ff_build_rac_states(RangeCoder *c, int factor, int max_p){
const int64_t one= 1LL<<32;
int64_t p;
int last_p8, p8, i;
memset(c->zero_state, 0, sizeof(c->zero_state));
memset(c-> one_state, 0, sizeof(c-> one_state));
last_p8= 0;
p= one/2;
for(i=0; i<128; i++){
p8= (256*p + one/2) >> 32; //FIXME try without the one
if(p8 <= last_p8) p8= last_p8+1;
if(last_p8 && last_p8<256 && p8<=max_p)
c->one_state[last_p8]= p8;
p+= ((one-p)*factor + one/2) >> 32;
last_p8= p8;
}
for(i=256-max_p; i<=max_p; i++){
if(c->one_state[i])
continue;
p= (i*one + 128) >> 8;
p+= ((one-p)*factor + one/2) >> 32;
p8= (256*p + one/2) >> 32; //FIXME try without the one
if(p8 <= i) p8= i+1;
if(p8 > max_p) p8= max_p;
c->one_state[ i]= p8;
}
for(i=1; i<255; i++)
c->zero_state[i]= 256-c->one_state[256-i];
}
/**
*
* @return the number of bytes written
*/
int ff_rac_terminate(RangeCoder *c){
c->range=0xFF;
c->low +=0xFF;
renorm_encoder(c);
c->range=0xFF;
renorm_encoder(c);
assert(c->low == 0);
assert(c->range >= 0x100);
return c->bytestream - c->bytestream_start;
}
#ifdef TEST
#define SIZE 10240
#include "libavutil/lfg.h"
int main(void){
RangeCoder c;
uint8_t b[9*SIZE];
uint8_t r[9*SIZE];
int i;
uint8_t state[10]= {0};
AVLFG prng;
av_lfg_init(&prng, 1);
ff_init_range_encoder(&c, b, SIZE);
ff_build_rac_states(&c, 0.05*(1LL<<32), 128+64+32+16);
memset(state, 128, sizeof(state));
for(i=0; i<SIZE; i++){
r[i] = av_lfg_get(&prng) % 7;
}
for(i=0; i<SIZE; i++){
START_TIMER
put_rac(&c, state, r[i]&1);
STOP_TIMER("put_rac")
}
ff_rac_terminate(&c);
ff_init_range_decoder(&c, b, SIZE);
memset(state, 128, sizeof(state));
for(i=0; i<SIZE; i++){
START_TIMER
if( (r[i]&1) != get_rac(&c, state) )
av_log(NULL, AV_LOG_DEBUG, "rac failure at %d\n", i);
STOP_TIMER("get_rac")
}
return 0;
}
#endif /* TEST */
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