1/* 2 * Lagged Fibonacci PRNG 3 * Copyright (c) 2008 Michael Niedermayer 4 * 5 * This file is part of FFmpeg. 6 * 7 * FFmpeg is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU Lesser General Public 9 * License as published by the Free Software Foundation; either 10 * version 2.1 of the License, or (at your option) any later version. 11 * 12 * FFmpeg is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 * Lesser General Public License for more details. 16 * 17 * You should have received a copy of the GNU Lesser General Public 18 * License along with FFmpeg; if not, write to the Free Software 19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 20 */ 21 22#include <inttypes.h> 23#include <limits.h> 24#include <math.h> 25#include "lfg.h" 26#include "md5.h" 27#include "intreadwrite.h" 28#include "attributes.h" 29 30av_cold void av_lfg_init(AVLFG *c, unsigned int seed) 31{ 32 uint8_t tmp[16] = { 0 }; 33 int i; 34 35 for (i = 8; i < 64; i += 4) { 36 AV_WL32(tmp, seed); 37 tmp[4] = i; 38 av_md5_sum(tmp, tmp, 16); 39 c->state[i ] = AV_RL32(tmp); 40 c->state[i + 1] = AV_RL32(tmp + 4); 41 c->state[i + 2] = AV_RL32(tmp + 8); 42 c->state[i + 3] = AV_RL32(tmp + 12); 43 } 44 c->index = 0; 45} 46 47void av_bmg_get(AVLFG *lfg, double out[2]) 48{ 49 double x1, x2, w; 50 51 do { 52 x1 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0; 53 x2 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0; 54 w = x1 * x1 + x2 * x2; 55 } while (w >= 1.0); 56 57 w = sqrt((-2.0 * log(w)) / w); 58 out[0] = x1 * w; 59 out[1] = x2 * w; 60} 61 62#ifdef TEST 63#include "log.h" 64#include "timer.h" 65 66int main(void) 67{ 68 int x = 0; 69 int i, j; 70 AVLFG state; 71 72 av_lfg_init(&state, 0xdeadbeef); 73 for (j = 0; j < 10000; j++) { 74 START_TIMER 75 for (i = 0; i < 624; i++) { 76 //av_log(NULL, AV_LOG_ERROR, "%X\n", av_lfg_get(&state)); 77 x += av_lfg_get(&state); 78 } 79 STOP_TIMER("624 calls of av_lfg_get"); 80 } 81 av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x); 82 83 /* BMG usage example */ 84 { 85 double mean = 1000; 86 double stddev = 53; 87 88 av_lfg_init(&state, 42); 89 90 for (i = 0; i < 1000; i += 2) { 91 double bmg_out[2]; 92 av_bmg_get(&state, bmg_out); 93 av_log(NULL, AV_LOG_INFO, 94 "%f\n%f\n", 95 bmg_out[0] * stddev + mean, 96 bmg_out[1] * stddev + mean); 97 } 98 } 99 100 return 0; 101} 102#endif 103