Home | History | Annotate | Download | only in util 
      1 #include <math.h>
      2 
      3 #include "stat.h"
      4 
      5 void 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 	if (val > stats->max)
     15 		stats->max = val;
     16 
     17 	if (val < stats->min)
     18 		stats->min = val;
     19 }
     20 
     21 double avg_stats(struct stats *stats)
     22 {
     23 	return stats->mean;
     24 }
     25 
     26 /*
     27  * http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance
     28  *
     29  *       (\Sum n_i^2) - ((\Sum n_i)^2)/n
     30  * s^2 = -------------------------------
     31  *                  n - 1
     32  *
     33  * http://en.wikipedia.org/wiki/Stddev
     34  *
     35  * The std dev of the mean is related to the std dev by:
     36  *
     37  *             s
     38  * s_mean = -------
     39  *          sqrt(n)
     40  *
     41  */
     42 double stddev_stats(struct stats *stats)
     43 {
     44 	double variance, variance_mean;
     45 
     46 	if (stats->n < 2)
     47 		return 0.0;
     48 
     49 	variance = stats->M2 / (stats->n - 1);
     50 	variance_mean = variance / stats->n;
     51 
     52 	return sqrt(variance_mean);
     53 }
     54 
     55 double rel_stddev_stats(double stddev, double avg)
     56 {
     57 	double pct = 0.0;
     58 
     59 	if (avg)
     60 		pct = 100.0 * stddev/avg;
     61 
     62 	return pct;
     63 }
     64