XorShift.java

package org.caudexorigo.jpt.sample;

import java.util.Random;

public class XorShift extends Random
{
	private static final long serialVersionUID = 6208727693524452904L;
	private long seed;

	/**
	 * Creates a new pseudo random number generator. The seed is initialized to the current time, as if by <code>setSeed(System.currentTimeMillis());</code>.
	 */
	public XorShift()
	{
		this(System.nanoTime());
	}

	/**
	 * Creates a new pseudo random number generator, starting with the specified seed, using <code>setSeed(seed);</code>.
	 * 
	 * @param seed
	 *            the initial seed
	 */
	public XorShift(long seed)
	{
		this.seed = seed;
	}

	/**
	 * Returns the current state of the seed, can be used to clone the object
	 * 
	 * @returns the current seed
	 */
	public synchronized long getSeed()
	{
		return seed;
	}

	/**
	 * Sets the seed for this pseudo random number generator. As described above, two instances of the same random class, starting with the same seed, produce the same results, if the same methods are called.
	 * 
	 * @param s
	 *            the new seed
	 */
	public synchronized void setSeed(long seed)
	{
		this.seed = seed;
		super.setSeed(seed);
	}

	/**
	 * Returns an XSRandom object with the same state as the original
	 */
	public XorShift clone()
	{
		return new XorShift(getSeed());
	}

	/**
	 * Implementation of George Marsaglia's elegant Xorshift random generator 30% faster and better quality than the built-in java.util.random see also see http://www.javamex.com/tutorials/random_numbers/xorshift.shtml
	 */
	protected int next(int nbits)
	{
		long x = seed;
		x ^= (x << 21);
		x ^= (x >>> 35);
		x ^= (x << 4);
		seed = x;
		x &= ((1L << nbits) - 1);
		return (int) x;
	}
}