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Linux/tools/perf/util/stat.c

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  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 

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