netem/paretonormal.c

   1 /*
   2  * Paretoormal distribution table generator
   3  *
   4  * This distribution is simply .25*normal + .75*pareto; a combination
   5  * which seems to match experimentally observed distributions reasonably
   6  *  well, but is computationally easy to handle.
   7  * The entries represent a scaled inverse of the cumulative distribution
   8  * function.
   9  *
  10  * Taken from the uncopyrighted NISTnet code.
  11  */
  12 #include <stdio.h>
  13 #include <stdlib.h>
  14 #include <string.h>
  15 #include <math.h>
  16 #include <limits.h>
  17 #include <malloc.h>
  18
  19 #include <linux/types.h>
  20 #include <linux/pkt_sched.h>
  21
  22 #define TABLESIZE       16384
  23 #define TABLEFACTOR     NETEM_DIST_SCALE
  24
  25 static double
  26 normal(double x, double mu, double sigma)
  27 {
  28         return .5 + .5*erf((x-mu)/(sqrt(2.0)*sigma));
  29 }
  30
  31 static const double a=3.0;
  32
  33 static int
  34 paretovalue(int i)
  35 {
  36         double dvalue;
  37
  38         i = 65536-4*i;
  39         dvalue = (double)i/(double)65536;
  40         dvalue = 1.0/pow(dvalue, 1.0/a);
  41         dvalue -= 1.5;
  42         dvalue *= (4.0/3.0)*(double)TABLEFACTOR;
  43         if (dvalue > 32767)
  44                 dvalue = 32767;
  45         return (int)rint(dvalue);
  46 }
  47
  48 int
  49 main(int argc, char **argv)
  50 {
  51         int i,n;
  52         double x;
  53         double table[TABLESIZE+1];
  54
  55         for (x = -10.0; x < 10.05; x += .00005) {
  56                 i = rint(TABLESIZE*normal(x, 0.0, 1.0));
  57                 table[i] = x;
  58         }
  59         printf(
  60 "# This is the distribution table for the paretonormal distribution.\n"
  61         );
  62
  63         for (i = n = 0; i < TABLESIZE; i += 4) {
  64                 int normvalue, parvalue, value;
  65
  66                 normvalue = (int) rint(table[i]*TABLEFACTOR);
  67                 parvalue = paretovalue(i);
  68
  69                 value = (normvalue+3*parvalue)/4;
  70                 if (value < SHRT_MIN) value = SHRT_MIN;
  71                 if (value > SHRT_MAX) value = SHRT_MAX;
  72
  73                 printf(" %d", value);
  74                 if (++n == 8) {
  75                         putchar('\n');
  76                         n = 0;
  77                 }
  78         }
  79
  80         return 0;
  81 }