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/*
 * 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 XORShift Algorithm Paper
 */
@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));
	}
}