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lfg.c
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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 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 
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 }
Definition: lfg.h:25
int index
Definition: lfg.h:27
uint64_t i
Definition: intfloat.h:33
Macro definitions for various function/variable attributes.
uint8_t
#define av_cold
Definition: attributes.h:82
void av_md5_sum(uint8_t *dst, const uint8_t *src, const int len)
Hash an array of data.
Definition: md5.c:207
void av_bmg_get(AVLFG *lfg, double out[2])
Get the next two numbers generated by a Box-Muller Gaussian generator using the random numbers issued...
Definition: lfg.c:47
static uint8_t tmp[8]
Definition: des-test.c:38
FILE * out
Definition: movenc-test.c:54
static unsigned int seed
Definition: videogen.c:78
static unsigned int av_lfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using an ALFG.
Definition: lfg.h:38
av_cold void av_lfg_init(AVLFG *c, unsigned int seed)
Definition: lfg.c:30
unsigned int state[64]
Definition: lfg.h:26
static double c[64]
uint64_t_TMPL AV_WL64 unsigned int_TMPL AV_RL32
Definition: bytestream.h:87
#define AV_WL32(p, v)
Definition: intreadwrite.h:426