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