Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
1#include <math.h>
2
3#include "stat.h"
4
5void update_stats(struct stats *stats, u64 val)
6{
7 double delta;
8
9 stats->n++;
10 delta = val - stats->mean;
11 stats->mean += delta / stats->n;
12 stats->M2 += delta*(val - stats->mean);
13}
14
15double avg_stats(struct stats *stats)
16{
17 return stats->mean;
18}
19
20/*
21 * http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance
22 *
23 * (\Sum n_i^2) - ((\Sum n_i)^2)/n
24 * s^2 = -------------------------------
25 * n - 1
26 *
27 * http://en.wikipedia.org/wiki/Stddev
28 *
29 * The std dev of the mean is related to the std dev by:
30 *
31 * s
32 * s_mean = -------
33 * sqrt(n)
34 *
35 */
36double stddev_stats(struct stats *stats)
37{
38 double variance, variance_mean;
39
40 if (!stats->n)
41 return 0.0;
42
43 variance = stats->M2 / (stats->n - 1);
44 variance_mean = variance / stats->n;
45
46 return sqrt(variance_mean);
47}
48
49double rel_stddev_stats(double stddev, double avg)
50{
51 double pct = 0.0;
52
53 if (avg)
54 pct = 100.0 * stddev/avg;
55
56 return pct;
57}