com.mchange.v2.util.XORShiftRandomUtils Maven / Gradle / Ivy
/*
* Distributed as part of mchange-commons-java v.0.2.3
*
* Copyright (C) 2012 Machinery For Change, Inc.
*
* Author: Steve Waldman
*
* This library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License version 2.1, as
* published by the Free Software Foundation.
*
* This software 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 software; see the file LICENSE. If not, write to the
* Free Software Foundation, Inc., 59 Temple Place, Suite 330,
* Boston, MA 02111-1307, USA.
*/
package com.mchange.v2.util;
/**
* A not-cryptographically-strong but decent and very fast
* pseudorandom number generator. Algorithm can be inlined easily
* for speed.
*
* Algorithm taken from...
*
* http://javamex.com/tutorials/random_numbers/xorshift.shtml
*
*/
public final class XORShiftRandomUtils
{
public static long nextLong(long prev)
{
prev ^= (prev << 21);
prev ^= (prev >>> 35);
prev ^= (prev << 4);
return prev;
}
public static void main(String[] argv)
{
long x = System.currentTimeMillis();
int len = 100;
int[] counts = new int[len];
for(int i = 0; i < 1000000; ++i)
{
x = nextLong(x);
++counts[ (int)(Math.abs(x) % len) ];
if ((i % 10000) == 0)
System.out.println( x );
}
for (int i = 0; i < len; ++i)
{
if (i != 0) System.out.print(", ");
System.out.print( i + " -> " + counts[i]);
}
System.out.println();
}
}