Implement av_bmg_next(), a Box-Muller Gaussian random generator.
[libav.git] / libavutil / lfg.h
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 #ifndef AVUTIL_LFG_H
23 #define AVUTIL_LFG_H
24
25 typedef struct {
26 unsigned int state[64];
27 int index;
28 } AVLFG;
29
30 void av_lfg_init(AVLFG *c, unsigned int seed);
31
32 /**
33 * Gets the next random unsigned 32-bit number using an ALFG.
34 *
35 * Please also consider a simple LCG like state= state*1664525+1013904223,
36 * it may be good enough and faster for your specific use case.
37 */
38 static inline unsigned int av_lfg_get(AVLFG *c){
39 c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];
40 return c->state[c->index++ & 63];
41 }
42
43 /**
44 * Gets the next random unsigned 32-bit number using a MLFG.
45 *
46 * Please also consider av_lfg_get() above, it is faster.
47 */
48 static inline unsigned int av_mlfg_get(AVLFG *c){
49 unsigned int a= c->state[(c->index-55) & 63];
50 unsigned int b= c->state[(c->index-24) & 63];
51 return c->state[c->index++ & 63] = 2*a*b+a+b;
52 }
53
54 /**
55 * Gets the next two numbers generated by a Box-Muller Gaussian
56 * generator using the random numbers issued by lfg.
57 *
58 * @param out[2] array where are placed the two generated numbers
59 */
60 void av_bmg_get(AVLFG *lfg, double out[2]);
61
62 #endif /* AVUTIL_LFG_H */