/* * Range coder * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at> * * This file is part of FFmpeg. * * FFmpeg 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. * * FFmpeg 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 FFmpeg; 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 */