HighQualityRandom.java

/**
 * 
 */
package org.feature.model.utilities;

import java.util.Random;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * According to the authors of 
 * Numerical Recipes: The Art of Scientific Computing
 * two XORShift generators are combined with an LCG and a multiply with carry generator.
 * taken from http://www.javamex.com/tutorials/random_numbers/numerical_recipes.shtml
 * 
 * @author <a href=mailto:info@juliaschroeter.de>Julia Schroeter</a>
 * 
 */
public class HighQualityRandom extends Random {

   /**
    * 
    */
   private static final long serialVersionUID = 1L;
   private Lock l = new ReentrantLock();
   private long u;
   private long v = 4101842887655102017L;
   private long w = 1;

   public HighQualityRandom() {
      this(System.nanoTime());
   }

   public HighQualityRandom(long seed) {
      l.lock();
      u = seed ^ v;
      nextLong();
      v = u;
      nextLong();
      w = v;
      nextLong();
      l.unlock();
   }

   public long nextLong() {
      l.lock();
      try {
         u = u * 2862933555777941757L + 7046029254386353087L;
         v ^= v >>> 17;
         v ^= v << 31;
         v ^= v >>> 8;
         w = 4294957665L * (w & 0xffffffff) + (w >>> 32);
         long x = u ^ (u << 21);
         x ^= x >>> 35;
         x ^= x << 4;
         long ret = (x + v) ^ w;
         return ret;
      }
      finally {
         l.unlock();
      }
   }

   protected int next(int bits) {
      return (int) (nextLong() >>> (64 - bits));
   }

}