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