yading@11: /*
yading@11:  * Lagged Fibonacci PRNG
yading@11:  * Copyright (c) 2008 Michael Niedermayer
yading@11:  *
yading@11:  * This file is part of FFmpeg.
yading@11:  *
yading@11:  * FFmpeg is free software; you can redistribute it and/or
yading@11:  * modify it under the terms of the GNU Lesser General Public
yading@11:  * License as published by the Free Software Foundation; either
yading@11:  * version 2.1 of the License, or (at your option) any later version.
yading@11:  *
yading@11:  * FFmpeg is distributed in the hope that it will be useful,
yading@11:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@11:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@11:  * Lesser General Public License for more details.
yading@11:  *
yading@11:  * You should have received a copy of the GNU Lesser General Public
yading@11:  * License along with FFmpeg; if not, write to the Free Software
yading@11:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@11:  */
yading@11: 
yading@11: #include <inttypes.h>
yading@11: #include <limits.h>
yading@11: #include <math.h>
yading@11: #include "lfg.h"
yading@11: #include "md5.h"
yading@11: #include "intreadwrite.h"
yading@11: #include "attributes.h"
yading@11: 
yading@11: av_cold void av_lfg_init(AVLFG *c, unsigned int seed)
yading@11: {
yading@11:     uint8_t tmp[16] = { 0 };
yading@11:     int i;
yading@11: 
yading@11:     for (i = 8; i < 64; i += 4) {
yading@11:         AV_WL32(tmp, seed);
yading@11:         tmp[4] = i;
yading@11:         av_md5_sum(tmp, tmp, 16);
yading@11:         c->state[i    ] = AV_RL32(tmp);
yading@11:         c->state[i + 1] = AV_RL32(tmp + 4);
yading@11:         c->state[i + 2] = AV_RL32(tmp + 8);
yading@11:         c->state[i + 3] = AV_RL32(tmp + 12);
yading@11:     }
yading@11:     c->index = 0;
yading@11: }
yading@11: 
yading@11: void av_bmg_get(AVLFG *lfg, double out[2])
yading@11: {
yading@11:     double x1, x2, w;
yading@11: 
yading@11:     do {
yading@11:         x1 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
yading@11:         x2 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
yading@11:         w  = x1 * x1 + x2 * x2;
yading@11:     } while (w >= 1.0);
yading@11: 
yading@11:     w = sqrt((-2.0 * log(w)) / w);
yading@11:     out[0] = x1 * w;
yading@11:     out[1] = x2 * w;
yading@11: }
yading@11: 
yading@11: #ifdef TEST
yading@11: #include "log.h"
yading@11: #include "timer.h"
yading@11: 
yading@11: int main(void)
yading@11: {
yading@11:     int x = 0;
yading@11:     int i, j;
yading@11:     AVLFG state;
yading@11: 
yading@11:     av_lfg_init(&state, 0xdeadbeef);
yading@11:     for (j = 0; j < 10000; j++) {
yading@11:         START_TIMER
yading@11:         for (i = 0; i < 624; i++) {
yading@11:             //av_log(NULL, AV_LOG_ERROR, "%X\n", av_lfg_get(&state));
yading@11:             x += av_lfg_get(&state);
yading@11:         }
yading@11:         STOP_TIMER("624 calls of av_lfg_get");
yading@11:     }
yading@11:     av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
yading@11: 
yading@11:     /* BMG usage example */
yading@11:     {
yading@11:         double mean   = 1000;
yading@11:         double stddev = 53;
yading@11: 
yading@11:         av_lfg_init(&state, 42);
yading@11: 
yading@11:         for (i = 0; i < 1000; i += 2) {
yading@11:             double bmg_out[2];
yading@11:             av_bmg_get(&state, bmg_out);
yading@11:             av_log(NULL, AV_LOG_INFO,
yading@11:                    "%f\n%f\n",
yading@11:                    bmg_out[0] * stddev + mean,
yading@11:                    bmg_out[1] * stddev + mean);
yading@11:         }
yading@11:     }
yading@11: 
yading@11:     return 0;
yading@11: }
yading@11: #endif