Statistics
| Branch: | Revision:

ffmpeg / libavutil / lfg.h @ 80a07f6e

History | View | Annotate | Download (1.94 KB)

1 2754fe8b Michael Niedermayer
/*
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 98790382 Stefano Sabatini
#ifndef AVUTIL_LFG_H
23
#define AVUTIL_LFG_H
24 2754fe8b Michael Niedermayer
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 2cf3c863 Michael Niedermayer
/**
33 89c9ff50 Diego Biurrun
 * Gets the next random unsigned 32-bit number using an ALFG.
34 2cf3c863 Michael Niedermayer
 *
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 2754fe8b Michael Niedermayer
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 310d4424 Michael Niedermayer
/**
44 89c9ff50 Diego Biurrun
 * Gets the next random unsigned 32-bit number using a MLFG.
45 310d4424 Michael Niedermayer
 *
46 89c9ff50 Diego Biurrun
 * Please also consider av_lfg_get() above, it is faster.
47 310d4424 Michael Niedermayer
 */
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 f39e8b03 Michael Niedermayer
    return c->state[c->index++ & 63] = 2*a*b+a+b;
52 310d4424 Michael Niedermayer
}
53
54 3ba69a15 Stefano Sabatini
/**
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 98790382 Stefano Sabatini
#endif /* AVUTIL_LFG_H */