b5db5a4b17cb0a4f091be007c5ed74db78038d1c
[libav.git] / libavutil / lfg.c
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
30 void av_cold av_lfg_init(AVLFG *c, unsigned int seed){
31 uint8_t tmp[16]={0};
32 int i;
33
34 for(i=8; i<64; i+=4){
35 AV_WL32(tmp, seed); tmp[4]=i;
36 av_md5_sum(tmp, tmp, 16);
37 c->state[i ]= AV_RL32(tmp);
38 c->state[i+1]= AV_RL32(tmp+4);
39 c->state[i+2]= AV_RL32(tmp+8);
40 c->state[i+3]= AV_RL32(tmp+12);
41 }
42 c->index=0;
43 }
44
45 void av_bmg_get(AVLFG *lfg, double out[2])
46 {
47 double x1, x2, w;
48
49 do {
50 x1 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0;
51 x2 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0;
52 w = x1*x1 + x2*x2;
53 } while (w >= 1.0);
54
55 w = sqrt((-2.0 * log(w)) / w);
56 out[0] = x1 * w;
57 out[1] = x2 * w;
58 }
59
60 #ifdef TEST
61 #include "log.h"
62 #include "timer.h"
63
64 int main(void)
65 {
66 int x=0;
67 int i, j;
68 AVLFG state;
69
70 av_lfg_init(&state, 0xdeadbeef);
71 for (j = 0; j < 10000; j++) {
72 START_TIMER
73 for (i = 0; i < 624; i++) {
74 // av_log(NULL,AV_LOG_ERROR, "%X\n", av_lfg_get(&state));
75 x+=av_lfg_get(&state);
76 }
77 STOP_TIMER("624 calls of av_lfg_get");
78 }
79 av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
80
81 /* BMG usage example */
82 {
83 double mean = 1000;
84 double stddev = 53;
85
86 av_lfg_init(&state, 42);
87
88 for (i = 0; i < 1000; i += 2) {
89 double bmg_out[2];
90 av_bmg_get(&state, bmg_out);
91 av_log(NULL, AV_LOG_INFO,
92 "%f\n%f\n",
93 bmg_out[0] * stddev + mean,
94 bmg_out[1] * stddev + mean);
95 }
96 }
97
98 return 0;
99 }
100 #endif