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 "lfg.h"
24#include "md5.h"
25#include "intreadwrite.h"
26#include "attributes.h"
27
28void av_cold av_lfg_init(AVLFG *c, unsigned int seed){
29    uint8_t tmp[16]={0};
30    int i;
31
32    for(i=8; i<64; i+=4){
33        AV_WL32(tmp, seed); tmp[4]=i;
34        av_md5_sum(tmp, tmp,  16);
35        c->state[i  ]= AV_RL32(tmp);
36        c->state[i+1]= AV_RL32(tmp+4);
37        c->state[i+2]= AV_RL32(tmp+8);
38        c->state[i+3]= AV_RL32(tmp+12);
39    }
40    c->index=0;
41}
42
43void av_bmg_get(AVLFG *lfg, double out[2])
44{
45    double x1, x2, w;
46
47    do {
48        x1 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0;
49        x2 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0;
50        w = x1*x1 + x2*x2;
51    } while (w >= 1.0);
52
53    w = sqrt((-2.0 * log(w)) / w);
54    out[0] = x1 * w;
55    out[1] = x2 * w;
56}
57
58#ifdef TEST
59#include "log.h"
60#include "timer.h"
61
62int main(void)
63{
64    int x=0;
65    int i, j;
66    AVLFG state;
67
68    av_lfg_init(&state, 0xdeadbeef);
69    for (j = 0; j < 10000; j++) {
70        START_TIMER
71        for (i = 0; i < 624; i++) {
72//            av_log(NULL,AV_LOG_ERROR, "%X\n", av_lfg_get(&state));
73            x+=av_lfg_get(&state);
74        }
75        STOP_TIMER("624 calls of av_lfg_get");
76    }
77    av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
78
79    /* BMG usage example */
80    {
81        double mean   = 1000;
82        double stddev = 53;
83
84        av_lfg_init(&state, 42);
85
86        for (i = 0; i < 1000; i += 2) {
87            double bmg_out[2];
88            av_bmg_get(&state, bmg_out);
89            av_log(NULL, AV_LOG_INFO,
90                   "%f\n%f\n",
91                   bmg_out[0] * stddev + mean,
92                   bmg_out[1] * stddev + mean);
93        }
94    }
95
96    return 0;
97}
98#endif
99