/* * Lagged Fibonacci PRNG * Copyright (c) 2008 Michael Niedermayer * * This file is part of Libav. * * Libav 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. * * Libav 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 Libav; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #include <inttypes.h> #include <limits.h> #include <math.h> #include "lfg.h" #include "md5.h" #include "intreadwrite.h" #include "attributes.h" void av_cold av_lfg_init(AVLFG *c, unsigned int seed) { uint8_t tmp[16] = { 0 }; int i; for (i = 8; i < 64; i += 4) { AV_WL32(tmp, seed); tmp[4] = i; av_md5_sum(tmp, tmp, 16); c->state[i ] = AV_RL32(tmp); c->state[i + 1] = AV_RL32(tmp + 4); c->state[i + 2] = AV_RL32(tmp + 8); c->state[i + 3] = AV_RL32(tmp + 12); } c->index = 0; } void av_bmg_get(AVLFG *lfg, double out[2]) { double x1, x2, w; do { x1 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0; x2 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0; w = x1 * x1 + x2 * x2; } while (w >= 1.0); w = sqrt((-2.0 * log(w)) / w); out[0] = x1 * w; out[1] = x2 * w; } #ifdef TEST #include "log.h" #include "timer.h" int main(void) { int x = 0; int i, j; AVLFG state; av_lfg_init(&state, 0xdeadbeef); for (j = 0; j < 10000; j++) { START_TIMER for (i = 0; i < 624; i++) { //av_log(NULL, AV_LOG_ERROR, "%X\n", av_lfg_get(&state)); x += av_lfg_get(&state); } STOP_TIMER("624 calls of av_lfg_get"); } av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x); /* BMG usage example */ { double mean = 1000; double stddev = 53; av_lfg_init(&state, 42); for (i = 0; i < 1000; i += 2) { double bmg_out[2]; av_bmg_get(&state, bmg_out); av_log(NULL, AV_LOG_INFO, "%f\n%f\n", bmg_out[0] * stddev + mean, bmg_out[1] * stddev + mean); } } return 0; } #endif