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libavcodec/rangecoder.c

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00001 /*
00002  * Range coder
00003  * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
00004  *
00005  * This file is part of FFmpeg.
00006  *
00007  * FFmpeg is free software; you can redistribute it and/or
00008  * modify it under the terms of the GNU Lesser General Public
00009  * License as published by the Free Software Foundation; either
00010  * version 2.1 of the License, or (at your option) any later version.
00011  *
00012  * FFmpeg is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015  * Lesser General Public License for more details.
00016  *
00017  * You should have received a copy of the GNU Lesser General Public
00018  * License along with FFmpeg; if not, write to the Free Software
00019  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00020  */
00021 
00034 #include <string.h>
00035 
00036 #include "avcodec.h"
00037 #include "rangecoder.h"
00038 #include "bytestream.h"
00039 
00040 
00041 void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size){
00042     c->bytestream_start=
00043     c->bytestream= buf;
00044     c->bytestream_end= buf + buf_size;
00045 
00046     c->low= 0;
00047     c->range= 0xFF00;
00048     c->outstanding_count= 0;
00049     c->outstanding_byte= -1;
00050 }
00051 
00052 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size){
00053     /* cast to avoid compiler warning */
00054     ff_init_range_encoder(c, (uint8_t *) buf, buf_size);
00055 
00056     c->low = bytestream_get_be16(&c->bytestream);
00057 }
00058 
00059 void ff_build_rac_states(RangeCoder *c, int factor, int max_p){
00060     const int64_t one= 1LL<<32;
00061     int64_t p;
00062     int last_p8, p8, i;
00063 
00064     memset(c->zero_state, 0, sizeof(c->zero_state));
00065     memset(c-> one_state, 0, sizeof(c-> one_state));
00066 
00067     last_p8= 0;
00068     p= one/2;
00069     for(i=0; i<128; i++){
00070         p8= (256*p + one/2) >> 32; //FIXME try without the one
00071         if(p8 <= last_p8) p8= last_p8+1;
00072         if(last_p8 && last_p8<256 && p8<=max_p)
00073             c->one_state[last_p8]= p8;
00074 
00075         p+= ((one-p)*factor + one/2) >> 32;
00076         last_p8= p8;
00077     }
00078 
00079     for(i=256-max_p; i<=max_p; i++){
00080         if(c->one_state[i])
00081             continue;
00082 
00083         p= (i*one + 128) >> 8;
00084         p+= ((one-p)*factor + one/2) >> 32;
00085         p8= (256*p + one/2) >> 32; //FIXME try without the one
00086         if(p8 <= i) p8= i+1;
00087         if(p8 > max_p) p8= max_p;
00088         c->one_state[    i]=     p8;
00089     }
00090 
00091     for(i=1; i<255; i++)
00092         c->zero_state[i]= 256-c->one_state[256-i];
00093 }
00094 
00099 int ff_rac_terminate(RangeCoder *c){
00100     c->range=0xFF;
00101     c->low +=0xFF;
00102     renorm_encoder(c);
00103     c->range=0xFF;
00104     renorm_encoder(c);
00105 
00106     assert(c->low   == 0);
00107     assert(c->range >= 0x100);
00108 
00109     return c->bytestream - c->bytestream_start;
00110 }
00111 
00112 #ifdef TEST
00113 #define SIZE 10240
00114 
00115 #include "libavutil/lfg.h"
00116 
00117 int main(void){
00118     RangeCoder c;
00119     uint8_t b[9*SIZE];
00120     uint8_t r[9*SIZE];
00121     int i;
00122     uint8_t state[10]= {0};
00123     AVLFG prng;
00124 
00125     av_lfg_init(&prng, 1);
00126 
00127     ff_init_range_encoder(&c, b, SIZE);
00128     ff_build_rac_states(&c, 0.05*(1LL<<32), 128+64+32+16);
00129 
00130     memset(state, 128, sizeof(state));
00131 
00132     for(i=0; i<SIZE; i++){
00133         r[i] = av_lfg_get(&prng) % 7;
00134     }
00135 
00136     for(i=0; i<SIZE; i++){
00137 START_TIMER
00138         put_rac(&c, state, r[i]&1);
00139 STOP_TIMER("put_rac")
00140     }
00141 
00142     ff_rac_terminate(&c);
00143 
00144     ff_init_range_decoder(&c, b, SIZE);
00145 
00146     memset(state, 128, sizeof(state));
00147 
00148     for(i=0; i<SIZE; i++){
00149 START_TIMER
00150         if( (r[i]&1) != get_rac(&c, state) )
00151             av_log(NULL, AV_LOG_DEBUG, "rac failure at %d\n", i);
00152 STOP_TIMER("get_rac")
00153     }
00154 
00155     return 0;
00156 }
00157 #endif /* TEST */

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