extendedrandom.java

peersim最新版1.0.4

/*
 * Copyright (c) 2003-2005 The BISON Project
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 */

package peersim.util;

import java.util.Random;
import java.lang.Math;

/**
 * Extends the functionality of <code>java.util.Random</code>.
 */
public class ExtendedRandom extends Random {

private long lastSeed;

// -------------------------------------------------------------------------

/** Calls super constructor. Also stores the seed to be returned by
{@link #getLastSeed}. */
public ExtendedRandom(long seed) {
	
	super(seed);
	lastSeed = seed;
}

// -------------------------------------------------------------------------

/**
 * Extracts the next integer, according to a Poisson distribution.
 * 
 * @param mean The mean of the Poisson distribution.
 * @return An integer Poisson extraction.
 */
public int nextPoisson(double mean) {
	
	double emean = Math.exp(-1 * mean);
	double product = 1;
	int count = 0;
	int result = 0;
	while (product >= emean) {
		product *= nextDouble();
		result = count;
		count++; // keep result one behind
	}
	return result;
}

// -------------------------------------------------------------------------

/**
* Implements nextLong(long) the same way nexInt(int) is implemented in
* java.util.Random.
* @param n the bound on the random number to be returned. Must be positive.
* @return a pseudorandom, uniformly distributed long value between 0
* (inclusive) and n (exclusive).
*/
public long nextLong(long n) {

	if (n<=0)
		throw new IllegalArgumentException("n must be positive");
	
	if ((n & -n) == n)  // i.e., n is a power of 2
	{	
		return nextLong()&(n-1);
	}
	
	long bits, val;
	do
	{
		bits = (nextLong()>>>1);
		val = bits % n;
	}
	while(bits - val + (n-1) < 0);
	
	return val;
}

// -------------------------------------------------------------------------

/** Sets random seed. Calls super method but also stores the seed to be
returned by {@link #getLastSeed}. */
public void setSeed( long seed ) {
	
	super.setSeed(seed);
	lastSeed = seed;
}

// -------------------------------------------------------------------------

/**
* Returns the last random seed that was set explicitly. Either at
* construction time or through {@link #setSeed}.
*/
public long getLastSeed() { return lastSeed; }

// -------------------------------------------------------------------------

/*
public static void main(String[] args) {

	ExtendedRandom er = new ExtendedRandom(12345678);
	for(int i=0; i<100; ++i)
		System.out.println(er.nextLong(Long.parseLong(args[0])));
	
}
*/
}