ffmpeg / libavutil / lfg.c @ f89c1402
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/*


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* Lagged Fibonacci PRNG

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* Copyright (c) 2008 Michael Niedermayer

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*

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* This file is part of FFmpeg.

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*

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* FFmpeg 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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* FFmpeg 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 FFmpeg; if not, write to the Free Software

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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 021101301 USA

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*/

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#include <inttypes.h> 
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#include "lfg.h" 
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#include "md5.h" 
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#include "intreadwrite.h" 
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void av_cold av_lfg_init(AVLFG *c, unsigned int seed){ 
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uint8_t tmp[16]={0}; 
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int i;

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for(i=8; i<64; i+=4){ 
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AV_WL32(tmp, seed); tmp[4]=i;

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av_md5_sum(tmp, tmp, 16);

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c>state[i ]= AV_RL32(tmp); 
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c>state[i+1]= AV_RL32(tmp+4); 
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c>state[i+2]= AV_RL32(tmp+8); 
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c>state[i+3]= AV_RL32(tmp+12); 
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} 
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c>index=0;

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} 
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void av_bmg_get(AVLFG *lfg, double out[2]) 
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{ 
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double x1, x2, w;

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do {

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x1 = 2.0/UINT_MAX*av_lfg_get(lfg)  1.0; 
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x2 = 2.0/UINT_MAX*av_lfg_get(lfg)  1.0; 
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w = x1*x1 + x2*x2; 
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} while (w >= 1.0); 
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w = sqrt((2.0 * log(w)) / w); 
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out[0] = x1 * w;

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out[1] = x2 * w;

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} 
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#ifdef TEST

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#include "log.h" 
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#include "common.h" 
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int main(void) 
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{ 
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int x=0; 
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int i, j;

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AVLFG state; 
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av_lfg_init(&state, 0xdeadbeef);

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for (j = 0; j < 10000; j++) { 
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START_TIMER 
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for (i = 0; i < 624; i++) { 
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// av_log(NULL,AV_LOG_ERROR, "%X\n", av_lfg_get(&state));

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x+=av_lfg_get(&state); 
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} 
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STOP_TIMER("624 calls of av_lfg_get");

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} 
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av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x); 
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/* BMG usage example */

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{ 
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double mean = 1000; 
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double stddev = 53; 
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av_lfg_init(&state, 42);

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for (i = 0; i < 1000; i += 2) { 
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double bmg_out[2]; 
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av_bmg_get(&state, bmg_out); 
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av_log(NULL, AV_LOG_INFO,

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"%f\n%f\n",

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bmg_out[0] * stddev + mean,

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bmg_out[1] * stddev + mean);

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} 
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} 
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return 0; 
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} 
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#endif
