jlibredis/src/main/java/redis/clients/util/MurmurHash.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 redis.clients.util;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;

/**
 * This is a very fast, non-cryptographic hash suitable for general hash-based
 * lookup. See http://murmurhash.googlepages.com/ for more details.
 * <p/>
 * <p>
 * The C version of MurmurHash 2.0 found at that site was ported to Java by
 * Andrzej Bialecki (ab at getopt org).
 * </p>
 */
public class MurmurHash implements Hashing {
    /**
     * Hashes bytes in an array.
     * 
     * @param data
     *            The bytes to hash.
     * @param seed
     *            The seed for the hash.
     * @return The 32 bit hash of the bytes in question.
     */
    public static int hash(byte[] data, int seed) {
	return hash(ByteBuffer.wrap(data), seed);
    }

    /**
     * Hashes bytes in part of an array.
     * 
     * @param data
     *            The data to hash.
     * @param offset
     *            Where to start munging.
     * @param length
     *            How many bytes to process.
     * @param seed
     *            The seed to start with.
     * @return The 32-bit hash of the data in question.
     */
    public static int hash(byte[] data, int offset, int length, int seed) {
	return hash(ByteBuffer.wrap(data, offset, length), seed);
    }

    /**
     * Hashes the bytes in a buffer from the current position to the limit.
     * 
     * @param buf
     *            The bytes to hash.
     * @param seed
     *            The seed for the hash.
     * @return The 32 bit murmur hash of the bytes in the buffer.
     */
    public static int hash(ByteBuffer buf, int seed) {
	// save byte order for later restoration
	ByteOrder byteOrder = buf.order();
	buf.order(ByteOrder.LITTLE_ENDIAN);

	int m = 0x5bd1e995;
	int r = 24;

	int h = seed ^ buf.remaining();

	int k;
	while (buf.remaining() >= 4) {
	    k = buf.getInt();

	    k *= m;
	    k ^= k >>> r;
	    k *= m;

	    h *= m;
	    h ^= k;
	}

	if (buf.remaining() > 0) {
	    ByteBuffer finish = ByteBuffer.allocate(4).order(
		    ByteOrder.LITTLE_ENDIAN);
	    // for big-endian version, use this first:
	    // finish.position(4-buf.remaining());
	    finish.put(buf).rewind();
	    h ^= finish.getInt();
	    h *= m;
	}

	h ^= h >>> 13;
	h *= m;
	h ^= h >>> 15;

	buf.order(byteOrder);
	return h;
    }

    public static long hash64A(byte[] data, int seed) {
	return hash64A(ByteBuffer.wrap(data), seed);
    }

    public static long hash64A(byte[] data, int offset, int length, int seed) {
	return hash64A(ByteBuffer.wrap(data, offset, length), seed);
    }

    public static long hash64A(ByteBuffer buf, int seed) {
	ByteOrder byteOrder = buf.order();
	buf.order(ByteOrder.LITTLE_ENDIAN);

	long m = 0xc6a4a7935bd1e995L;
	int r = 47;

	long h = seed ^ (buf.remaining() * m);

	long k;
	while (buf.remaining() >= 8) {
	    k = buf.getLong();

	    k *= m;
	    k ^= k >>> r;
	    k *= m;

	    h ^= k;
	    h *= m;
	}

	if (buf.remaining() > 0) {
	    ByteBuffer finish = ByteBuffer.allocate(8).order(
		    ByteOrder.LITTLE_ENDIAN);
	    // for big-endian version, do this first:
	    // finish.position(8-buf.remaining());
	    finish.put(buf).rewind();
	    h ^= finish.getLong();
	    h *= m;
	}

	h ^= h >>> r;
	h *= m;
	h ^= h >>> r;

	buf.order(byteOrder);
	return h;
    }

    public long hash(byte[] key) {
	return hash64A(key, 0x1234ABCD);
    }

    public long hash(String key) {
	return hash(SafeEncoder.encode(key));
    }
}