Murmur3_32.java

/*
 * 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.graph.utils;

import java.io.Serializable;

/**
 * A resettable implementation of the 32-bit MurmurHash algorithm.
 */
public class Murmur3_32 implements Serializable {

	private static final long serialVersionUID = 1L;

	// initial seed, which can be reset
	private final int seed;

	// number of 32-bit values processed
	private int count;

	// in-progress hash value
	private int hash;

	/**
	 * A resettable implementation of the 32-bit MurmurHash algorithm.
	 *
	 * @param seed MurmurHash seed
	 */
	public Murmur3_32(int seed) {
		this.seed = seed;
		reset();
	}

	/**
	 * Re-initialize the MurmurHash state.
	 *
	 * @return this
	 */
	public Murmur3_32 reset() {
		count = 0;
		hash = seed;
		return this;
	}

	/**
	 * Process a {@code double} value.
	 *
	 * @param input 64-bit input value
	 * @return this
	 */
	public Murmur3_32 hash(double input) {
		hash(Double.doubleToLongBits(input));
		return this;
	}

	/**
	 * Process a {@code float} value.
	 *
	 * @param input 32-bit input value
	 * @return this
	 */
	public Murmur3_32 hash(float input) {
		hash(Float.floatToIntBits(input));
		return this;
	}

	/**
	 * Process an {@code integer} value.
	 *
	 * @param input 32-bit input value
	 * @return this
	 */
	public Murmur3_32 hash(int input) {
		count++;

		input *= 0xcc9e2d51;
		input = Integer.rotateLeft(input, 15);
		input *= 0x1b873593;

		hash ^= input;
		hash = Integer.rotateLeft(hash, 13);
		hash = hash * 5 + 0xe6546b64;

		return this;
	}

	/**
	 * Process a {@code long} value.
	 *
	 * @param input 64-bit input value
	 * @return this
	 */
	public Murmur3_32 hash(long input) {
		hash((int)(input >>> 32));
		hash((int)input);
		return this;
	}

	/**
	 * Finalize and return the MurmurHash output.
	 *
	 * @return 32-bit hash
	 */
	public int hash() {
		hash ^= 4 * count;
		hash ^= hash >>> 16;
		hash *= 0x85ebca6b;
		hash ^= hash >>> 13;
		hash *= 0xc2b2ae35;
		hash ^= hash >>> 16;

		return hash;
	}
}