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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 }
61 
62 #ifdef TEST
63 #include "log.h"
64 #include "timer.h"
65 
66 int main(void)
67 {
68  int x = 0;
69  int i, j;
70  AVLFG state;
71 
72  av_lfg_init(&state, 0xdeadbeef);
73  for (j = 0; j < 10000; j++) {
75  for (i = 0; i < 624; i++) {
76  //av_log(NULL, AV_LOG_ERROR, "%X\n", av_lfg_get(&state));
77  x += av_lfg_get(&state);
78  }
79  STOP_TIMER("624 calls of av_lfg_get");
80  }
81  av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
82 
83  /* BMG usage example */
84  {
85  double mean = 1000;
86  double stddev = 53;
87  double samp_mean = 0.0, samp_stddev = 0.0;
88  double samp0, samp1;
89 
90  av_lfg_init(&state, 42);
91 
92  for (i = 0; i < 1000; i += 2) {
93  double bmg_out[2];
94  av_bmg_get(&state, bmg_out);
95  samp0 = bmg_out[0] * stddev + mean;
96  samp1 = bmg_out[1] * stddev + mean;
97  samp_mean += samp0 + samp1;
98  samp_stddev += samp0 * samp0 + samp1 * samp1;
100  "%f\n%f\n",
101  samp0,
102  samp1);
103  }
104  /* TODO: add proper normality test */
105  samp_mean /= 1000;
106  samp_stddev /= 999;
107  samp_stddev -= (1000.0/999.0)*samp_mean*samp_mean;
108  samp_stddev = sqrt(samp_stddev);
109  av_log(NULL, AV_LOG_INFO, "sample mean : %f\n"
110  "true mean : %f\n"
111  "sample stddev: %f\n"
112  "true stddev : %f\n",
113  samp_mean, mean, samp_stddev, stddev);
114  }
115 
116  return 0;
117 }
118 #endif
Definition: lfg.h:25
#define NULL
Definition: coverity.c:32
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
#define av_log(a,...)
#define AV_LOG_ERROR
Something went wrong and cannot losslessly be recovered.
Definition: log.h:176
FILE * out
Definition: movenc-test.c:54
#define AV_LOG_INFO
Standard information.
Definition: log.h:187
#define START_TIMER
Definition: timer.h:94
static unsigned int seed
Definition: videogen.c:78
static struct @211 state
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]
#define STOP_TIMER(id)
Definition: timer.h:95
int main(int argc, char **argv)
Definition: main.c:22
uint64_t_TMPL AV_WL64 unsigned int_TMPL AV_RL32
Definition: bytestream.h:87
#define AV_WL32(p, v)
Definition: intreadwrite.h:426