/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.flink.util;
import org.apache.flink.annotation.Public;
import java.util.Random;
/**
* Implement a random number generator based on the XORShift algorithm discovered by George Marsaglia.
* This RNG is observed 4.5 times faster than {@link java.util.Random} in benchmark, with the cost
* that abandon thread-safety. So it's recommended to create a new {@link XORShiftRandom} for each
* thread.
*
* @see <a href="http://www.jstatsoft.org/v08/i14/paper">XORShift Algorithm Paper</a>
*/
@Public
public class XORShiftRandom extends Random {
private static final long serialVersionUID = -825722456120842841L;
private long seed;
public XORShiftRandom() {
this(System.nanoTime());
}
public XORShiftRandom(long input) {
super(input);
this.seed = MathUtils.murmurHash((int) input) ^ MathUtils.murmurHash((int) (input >>> 32));
}
/**
* All other methods like nextInt()/nextDouble()... depends on this, so we just need to overwrite
* this.
*
* @param bits Random bits
* @return The next pseudorandom value from this random number
* generator's sequence
*/
@Override
public int next(int bits) {
long nextSeed = seed ^ (seed << 21);
nextSeed ^= (nextSeed >>> 35);
nextSeed ^= (nextSeed << 4);
seed = nextSeed;
return (int) (nextSeed & ((1L << bits) - 1));
}
}