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
av_lfg_init(AVLFG * c,unsigned int seed)30 av_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
av_bmg_get(AVLFG * lfg,double out[2])47 void 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
main(void)66 int 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