netem/stats.c

   1 /*
   2  * Experimental data  distribution table generator
   3  * Taken from the uncopyrighted NISTnet code (public domain).
   4  *
   5  * Rread in a series of "random" data values, either
   6  * experimentally or generated from some probability distribution.
   7  * From this, report statistics.
   8  */
   9
  10 #include <stdio.h>
  11 #include <stdlib.h>
  12 #include <math.h>
  13 #include <malloc.h>
  14 #include <sys/types.h>
  15 #include <sys/stat.h>
  16
  17 void
  18 stats(FILE *fp)
  19 {
  20         struct stat info;
  21         double *x;
  22         int limit;
  23         int n=0, i;
  24         double mu=0.0, sigma=0.0, sumsquare=0.0, sum=0.0, top=0.0, rho=0.0;
  25         double sigma2=0.0;
  26
  27         fstat(fileno(fp), &info);
  28         if (info.st_size > 0) {
  29                 limit = 2*info.st_size/sizeof(double);  /* @@ approximate */
  30         } else {
  31                 limit = 10000;
  32         }
  33         x = (double *)malloc(limit*sizeof(double));
  34
  35         for (i=0; i<limit; ++i){
  36                 fscanf(fp, "%lf", &x[i]);
  37                 if (feof(fp))
  38                         break;
  39                 sumsquare += x[i]*x[i];
  40                 sum += x[i];
  41                 ++n;
  42         }
  43         mu = sum/(double)n;
  44         sigma = sqrt((sumsquare - (double)n*mu*mu)/(double)(n-1));
  45
  46         for (i=1; i < n; ++i){
  47                 top += ((double)x[i]-mu)*((double)x[i-1]-mu);
  48                 sigma2 += ((double)x[i-1] - mu)*((double)x[i-1] - mu);
  49
  50         }
  51         rho = top/sigma2;
  52
  53         printf("mu =    %12.6f\n", mu);
  54         printf("sigma = %12.6f\n", sigma);
  55         printf("rho =   %12.6f\n", rho);
  56         /*printf("sigma2 = %10.4f\n", sqrt(sigma2/(double)(n-1)));*/
  57         /*printf("correlation rho = %10.6f\n", top/((double)(n-1)*sigma*sigma));*/
  58 }
  59
  60
  61 int
  62 main(int argc, char **argv)
  63 {
  64         FILE *fp;
  65
  66         if (argc > 1) {
  67                 fp = fopen(argv[1], "r");
  68                 if (!fp) {
  69                         perror(argv[1]);
  70                         exit(1);
  71                 }
  72         } else {
  73                 fp = stdin;
  74         }
  75         stats(fp);
  76         return 0;
  77 }