Blame netem/paretonormal.c

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/*
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 * Paretoormal distribution table generator
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 *
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 * This distribution is simply .25*normal + .75*pareto; a combination
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 * which seems to match experimentally observed distributions reasonably
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 *  well, but is computationally easy to handle.
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 * The entries represent a scaled inverse of the cumulative distribution
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 * function.
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 *
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 * Taken from the uncopyrighted NISTnet code.
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 */
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <math.h>
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#include <limits.h>
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#include <malloc.h>
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#include <linux/types.h>
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#include <linux/pkt_sched.h>
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#define TABLESIZE	16384
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#define TABLEFACTOR	NETEM_DIST_SCALE
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static double
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normal(double x, double mu, double sigma)
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{
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	return .5 + .5*erf((x-mu)/(sqrt(2.0)*sigma));
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}
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static const double a=3.0;
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static int
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paretovalue(int i)
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{
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	double dvalue;
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	i = 65536-4*i;
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	dvalue = (double)i/(double)65536;
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	dvalue = 1.0/pow(dvalue, 1.0/a);
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	dvalue -= 1.5;
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	dvalue *= (4.0/3.0)*(double)TABLEFACTOR;
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	if (dvalue > 32767)
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		dvalue = 32767;
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	return (int)rint(dvalue);
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}
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int
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main(int argc, char **argv)
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{
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	int i,n;
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	double x;
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	double table[TABLESIZE+1];
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	for (x = -10.0; x < 10.05; x += .00005) {
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		i = rint(TABLESIZE*normal(x, 0.0, 1.0));
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		table[i] = x;
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	}
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	printf(
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"# This is the distribution table for the paretonormal distribution.\n"
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	);
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	for (i = n = 0; i < TABLESIZE; i += 4) {
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		int normvalue, parvalue, value;
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		normvalue = (int) rint(table[i]*TABLEFACTOR);
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		parvalue = paretovalue(i);
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		value = (normvalue+3*parvalue)/4;
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		if (value < SHRT_MIN) value = SHRT_MIN;
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		if (value > SHRT_MAX) value = SHRT_MAX;
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		printf(" %d", value);
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		if (++n == 8) {
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			putchar('\n');
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			n = 0;
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		}
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	}
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	return 0;
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}