FFmpeg
lfg.c
Go to the documentation of this file.
1 /*
2  * This file is part of FFmpeg.
3  *
4  * FFmpeg is free software; you can redistribute it and/or
5  * modify it under the terms of the GNU Lesser General Public
6  * License as published by the Free Software Foundation; either
7  * version 2.1 of the License, or (at your option) any later version.
8  *
9  * FFmpeg is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12  * Lesser General Public License for more details.
13  *
14  * You should have received a copy of the GNU Lesser General Public
15  * License along with FFmpeg; if not, write to the Free Software
16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
17  */
18 
19 #include "libavutil/log.h"
20 #include "libavutil/timer.h"
21 #include "libavutil/lfg.h"
22 
23 static const double Z_TABLE[31][10] = {
24  {0.5000, 0.5040, 0.5080, 0.5120, 0.5160, 0.5199, 0.5239, 0.5279, 0.5319, 0.5359},
25  {0.5398, 0.5438, 0.5478, 0.5517, 0.5557, 0.5596, 0.5636, 0.5675, 0.5714, 0.5753},
26  {0.5793, 0.5832, 0.5871, 0.5910, 0.5948, 0.5987, 0.6026, 0.6064, 0.6103, 0.6141},
27  {0.6179, 0.6217, 0.6255, 0.6293, 0.6331, 0.6368, 0.6406, 0.6443, 0.6480, 0.6517},
28  {0.6554, 0.6591, 0.6628, 0.6664, 0.6700, 0.6736, 0.6772, 0.6808, 0.6844, 0.6879},
29  {0.6915, 0.6950, 0.6985, 0.7019, 0.7054, 0.7088, 0.7123, 0.7157, 0.7190, 0.7224},
30  {0.7257, 0.7291, 0.7324, 0.7357, 0.7389, 0.7422, 0.7454, 0.7486, 0.7517, 0.7549},
31  {0.7580, 0.7611, 0.7642, 0.7673, 0.7704, 0.7734, 0.7764, 0.7794, 0.7823, 0.7852},
32  {0.7881, 0.7910, 0.7939, 0.7967, 0.7995, 0.8023, 0.8051, 0.8078, 0.8106, 0.8133},
33  {0.8159, 0.8186, 0.8212, 0.8238, 0.8264, 0.8289, 0.8315, 0.8340, 0.8365, 0.8389},
34  {0.8413, 0.8438, 0.8461, 0.8485, 0.8508, 0.8531, 0.8554, 0.8577, 0.8599, 0.8621},
35  {0.8643, 0.8665, 0.8686, 0.8708, 0.8729, 0.8749, 0.8770, 0.8790, 0.8810, 0.8830},
36  {0.8849, 0.8869, 0.8888, 0.8907, 0.8925, 0.8944, 0.8962, 0.8980, 0.8997, 0.9015},
37  {0.9032, 0.9049, 0.9066, 0.9082, 0.9099, 0.9115, 0.9131, 0.9147, 0.9162, 0.9177},
38  {0.9192, 0.9207, 0.9222, 0.9236, 0.9251, 0.9265, 0.9279, 0.9292, 0.9306, 0.9319},
39  {0.9332, 0.9345, 0.9357, 0.9370, 0.9382, 0.9394, 0.9406, 0.9418, 0.9429, 0.9441},
40  {0.9452, 0.9463, 0.9474, 0.9484, 0.9495, 0.9505, 0.9515, 0.9525, 0.9535, 0.9545},
41  {0.9554, 0.9564, 0.9573, 0.9582, 0.9591, 0.9599, 0.9608, 0.9616, 0.9625, 0.9633},
42  {0.9641, 0.9649, 0.9656, 0.9664, 0.9671, 0.9678, 0.9686, 0.9693, 0.9699, 0.9706},
43  {0.9713, 0.9719, 0.9726, 0.9732, 0.9738, 0.9744, 0.9750, 0.9756, 0.9761, 0.9767},
44  {0.9772, 0.9778, 0.9783, 0.9788, 0.9793, 0.9798, 0.9803, 0.9808, 0.9812, 0.9817},
45  {0.9821, 0.9826, 0.9830, 0.9834, 0.9838, 0.9842, 0.9846, 0.9850, 0.9854, 0.9857},
46  {0.9861, 0.9864, 0.9868, 0.9871, 0.9875, 0.9878, 0.9881, 0.9884, 0.9887, 0.9890},
47  {0.9893, 0.9896, 0.9898, 0.9901, 0.9904, 0.9906, 0.9909, 0.9911, 0.9913, 0.9916},
48  {0.9918, 0.9920, 0.9922, 0.9925, 0.9927, 0.9929, 0.9931, 0.9932, 0.9934, 0.9936},
49  {0.9938, 0.9940, 0.9941, 0.9943, 0.9945, 0.9946, 0.9948, 0.9949, 0.9951, 0.9952},
50  {0.9953, 0.9955, 0.9956, 0.9957, 0.9959, 0.9960, 0.9961, 0.9962, 0.9963, 0.9964},
51  {0.9965, 0.9966, 0.9967, 0.9968, 0.9969, 0.9970, 0.9971, 0.9972, 0.9973, 0.9974},
52  {0.9974, 0.9975, 0.9976, 0.9977, 0.9977, 0.9978, 0.9979, 0.9979, 0.9980, 0.9981},
53  {0.9981, 0.9982, 0.9982, 0.9983, 0.9984, 0.9984, 0.9985, 0.9985, 0.9986, 0.9986},
54  {0.9987, 0.9987, 0.9987, 0.9988, 0.9988, 0.9989, 0.9989, 0.9989, 0.9990, 0.9990} };
55 
56 // Inverse cumulative distribution function
57 static double inv_cdf(double u)
58 {
59  const double a[4] = { 2.50662823884,
60  -18.61500062529,
61  41.39119773534,
62  -25.44106049637};
63 
64  const double b[4] = {-8.47351093090,
65  23.08336743743,
66  -21.06224101826,
67  3.13082909833};
68 
69  const double c[9] = {0.3374754822726147,
70  0.9761690190917186,
71  0.1607979714918209,
72  0.0276438810333863,
73  0.0038405729373609,
74  0.0003951896511919,
75  0.0000321767881768,
76  0.0000002888167364,
77  0.0000003960315187};
78 
79  double r;
80  double x = u - 0.5;
81 
82  // Beasley-Springer
83  if (fabs(x) < 0.42) {
84 
85  double y = x * x;
86  r = x * (((a[3]*y+a[2])*y+a[1])*y+a[0]) /
87  ((((b[3]*y+b[2])*y+b[1])*y+b[0])*y+1.0);
88  }
89  else {// Moro
90  r = u;
91  if (x > 0.0)
92  r = 1.0 - u;
93  r = log(-log(r));
94  r = c[0] + r*(c[1]+r*(c[2]+r*(c[3]+r*(c[4]+r*(c[5]+r*(c[6]+
95  r*(c[7]+r*c[8])))))));
96  if (x < 0.0)
97  r = -r;
98  }
99 
100  return r;
101 }
102 int main(void)
103 {
104  int x = 0;
105  int i, j;
106  AVLFG state;
107  av_lfg_init(&state, 0xdeadbeef);
108  for (j = 0; j < 10000; j++) {
109  for (i = 0; i < 624; i++) {
110  //av_log(NULL, AV_LOG_ERROR, "%X\n", av_lfg_get(&state));
111  x += av_lfg_get(&state);
112  }
113  }
114  av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
115 
116  /* BMG usage example */
117  {
118  double mean = 1000;
119  double stddev = 53;
120  double samp_mean = 0.0, samp_stddev = 0.0, QH = 0;
121  double Z, p_value = -1, tot_samp = 1000;
122  double *PRN_arr = av_malloc_array(tot_samp, sizeof(double));
123 
124  if (!PRN_arr) {
125  fprintf(stderr, "failed to allocate memory!\n");
126  return 1;
127  }
128 
129  av_lfg_init(&state, 42);
130  for (i = 0; i < tot_samp; i += 2) {
131  double bmg_out[2];
132  av_bmg_get(&state, bmg_out);
133  PRN_arr[i ] = bmg_out[0] * stddev + mean;
134  PRN_arr[i+1] = bmg_out[1] * stddev + mean;
135  samp_mean += PRN_arr[i] + PRN_arr[i+1];
136  samp_stddev += PRN_arr[i] * PRN_arr[i] + PRN_arr[i+1] * PRN_arr[i+1];
137  printf("PRN%d : %f\n"
138  "PRN%d : %f\n",
139  i, PRN_arr[i], i+1, PRN_arr[i+1]);
140  }
141  samp_mean /= tot_samp;
142  samp_stddev /= (tot_samp - 1);
143  samp_stddev -= (tot_samp * 1.0 / (tot_samp - 1))*samp_mean*samp_mean;
144  samp_stddev = sqrt(samp_stddev);
145  Z = (mean - samp_mean) / (stddev / sqrt(tot_samp));
146  {
147  int x, y, a, b, flag = 0;
148 
149  if (Z < 0.0) {
150  flag = !flag;
151  Z = Z * -1.0;
152  }
153 
154  a = (int)(Z * 100);
155  b = ((int)Z * 100);
156  x = Z * 10;
157  y = (b > 0) ? a % b : a;
158  y = y % 10;
159  if (x > 30 || y > 9) {
160  av_log(NULL, AV_LOG_INFO, "error: out of bounds! tried to access"
161  "Z_TABLE[%d][%d]\n", x, y);
162  goto SKIP;
163  }
164  p_value = flag ? 1 - Z_TABLE[x][y] : Z_TABLE[x][y];
165  }
166 
167 SKIP: for (i = 0; i < tot_samp; ++i) {
168 
169  if ( i < (tot_samp - 1)) {
170  double H_diff;
171  H_diff = inv_cdf((i + 2.0 - (3.0/8.0)) / (tot_samp + (1.0/4.0)));
172  H_diff -= inv_cdf((i + 1.0 - (3.0/8.0)) / (tot_samp + (1.0/4.0)));
173 
174  QH += ((PRN_arr[i + 1] - PRN_arr[i]) / H_diff);
175  }
176  }
177  QH = 1.0 - QH / ((tot_samp - 1.0) * samp_stddev);
178 
179  printf("sample mean : %f\n"
180  "true mean : %f\n"
181  "sample stddev: %f\n"
182  "true stddev : %f\n"
183  "z-score : %f\n"
184  "p-value : %f\n"
185  "QH[normality]: %f\n",
186  samp_mean, mean, samp_stddev, stddev, Z, p_value, QH);
187 
188  av_freep(&PRN_arr);
189  }
190  return 0;
191 }
AVLFG
Context structure for the Lagged Fibonacci PRNG.
Definition: lfg.h:33
NULL
#define NULL
Definition: coverity.c:32
a
The reader does not expect b to be semantically here and if the code is changed by maybe adding a a division or other the signedness will almost certainly be mistaken To avoid this confusion a new type was SUINT is the C unsigned type but it holds a signed int to use the same example SUINT a
Definition: undefined.txt:36
c
Undefined Behavior In the C some operations are like signed integer dereferencing freed accessing outside allocated Undefined Behavior must not occur in a C it is not safe even if the output of undefined operations is unused The unsafety may seem nit picking but Optimizing compilers have in fact optimized code on the assumption that no undefined Behavior occurs Optimizing code based on wrong assumptions can and has in some cases lead to effects beyond the output of computations The signed integer overflow problem in speed critical code Code which is highly optimized and works with signed integers sometimes has the problem that often the output of the computation does not c
Definition: undefined.txt:32
u
#define u(width, name, range_min, range_max)
Definition: cbs_h2645.c:264
av_bmg_get
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:49
timer.h
high precision timer, useful to profile code
state
static struct @321 state
av_log
#define av_log(a,...)
Definition: tableprint_vlc.h:28
AV_LOG_ERROR
#define AV_LOG_ERROR
Something went wrong and cannot losslessly be recovered.
Definition: log.h:194
fabs
static __device__ float fabs(float a)
Definition: cuda_runtime.h:182
r
const char * r
Definition: vf_curves.c:116
mean
static float mean(const float *input, int size)
Definition: vf_nnedi.c:864
b
#define b
Definition: input.c:41
AV_LOG_INFO
#define AV_LOG_INFO
Standard information.
Definition: log.h:205
av_lfg_get
static unsigned int av_lfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using an ALFG.
Definition: lfg.h:53
av_lfg_init
av_cold void av_lfg_init(AVLFG *c, unsigned int seed)
Definition: lfg.c:32
int
int
Definition: ffmpeg_filter.c:170
flag
#define flag(name)
Definition: cbs_av1.c:553
inv_cdf
static double inv_cdf(double u)
Definition: lfg.c:57
printf
printf("static const uint8_t my_array[100] = {\n")
av_freep
#define av_freep(p)
Definition: tableprint_vlc.h:35
av_malloc_array
#define av_malloc_array(a, b)
Definition: tableprint_vlc.h:32
main
int main(void)
Definition: lfg.c:102
i
int i
Definition: input.c:407
Z_TABLE
static const double Z_TABLE[31][10]
Definition: lfg.c:23
Generated on Mon Mar 8 2021 19:22:25 for FFmpeg by   doxygen 1.8.11