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101 lines
2.5 KiB
C
101 lines
2.5 KiB
C
/*
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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 02110-1301 USA
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*/
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#include <inttypes.h>
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#include <limits.h>
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#include <math.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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#include "attributes.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 "timer.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
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