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/libavutil/lfg.h

http://github.com/FFmpeg/FFmpeg
C Header | 80 lines | 23 code | 9 blank | 48 comment | 0 complexity | 4ac8ce4c1133afa0b0f08e25d41e7fb5 MD5 | raw file
 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#include <stdint.h>
26
27/**
28 * Context structure for the Lagged Fibonacci PRNG.
29 * The exact layout, types and content of this struct may change and should
30 * not be accessed directly. Only its sizeof() is guranteed to stay the same
31 * to allow easy instanciation.
32 */
33typedef struct AVLFG {
34    unsigned int state[64];
35    int index;
36} AVLFG;
37
38void av_lfg_init(AVLFG *c, unsigned int seed);
39
40/**
41 * Seed the state of the ALFG using binary data.
42 *
43 * Return value: 0 on success, negative value (AVERROR) on failure.
44 */
45int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length);
46
47/**
48 * Get the next random unsigned 32-bit number using an ALFG.
49 *
50 * Please also consider a simple LCG like state= state*1664525+1013904223,
51 * it may be good enough and faster for your specific use case.
52 */
53static inline unsigned int av_lfg_get(AVLFG *c){
54    unsigned a = c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];
55    c->index += 1U;
56    return a;
57}
58
59/**
60 * Get the next random unsigned 32-bit number using a MLFG.
61 *
62 * Please also consider av_lfg_get() above, it is faster.
63 */
64static inline unsigned int av_mlfg_get(AVLFG *c){
65    unsigned int a= c->state[(c->index-55) & 63];
66    unsigned int b= c->state[(c->index-24) & 63];
67    a = c->state[c->index & 63] = 2*a*b+a+b;
68    c->index += 1U;
69    return a;
70}
71
72/**
73 * Get the next two numbers generated by a Box-Muller Gaussian
74 * generator using the random numbers issued by lfg.
75 *
76 * @param out array where the two generated numbers are placed
77 */
78void av_bmg_get(AVLFG *lfg, double out[2]);
79
80#endif /* AVUTIL_LFG_H */