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 com.nearinfinity.bloomfilter;

/**
 * This is a very fast, non-cryptographic hash suitable for general hash-based
 * lookup. See http://murmurhash.googlepages.com/ for more details.
 * 
 * <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 {
	public static int hash(int seed, byte[] data, int offset, int length) {
		if (offset == 0) {
			return hash(seed,data,length);
		}
		int m = 0x5bd1e995;
		int r = 24;
		int h = seed ^ length;
		int len = length;
		int len_4 = len >> 2;
		for (int i = 0; i < len_4; i++) {
			int i_4 = i << 2;
			int offset_i_4 = offset + i_4;
			int k = data[offset_i_4 + 3];
			k = k << 8;
			k = k | (data[offset_i_4 + 2] & 0xff);
			k = k << 8;
			k = k | (data[offset_i_4 + 1] & 0xff);
			k = k << 8;
			k = k | (data[offset_i_4 + 0] & 0xff);
			k *= m;
			k ^= k >>> r;
			k *= m;
			h *= m;
			h ^= k;
		}
		int len_m = len_4 << 2;
		int left = len - len_m;
		if (left != 0) {
			int offset_len = len + offset;
			if (left >= 3) {
				h ^= (int) data[offset_len - 3] << 16;
			}
			if (left >= 2) {
				h ^= (int) data[offset_len - 2] << 8;
			}
			if (left >= 1) {
				h ^= (int) data[offset_len - 1];
			}
			h *= m;
		}
		h ^= h >>> 13;
		h *= m;
		h ^= h >>> 15;
		return h;
	}
	
	public static int hash(int seed, byte[] data, int length) {
		int m = 0x5bd1e995;
		int r = 24;
		int h = seed ^ length;
		int len = length;
		int len_4 = len >> 2;
		for (int i = 0; i < len_4; i++) {
			int i_4 = i << 2;
			int k = data[i_4 + 3];
			k = k << 8;
			k = k | (data[i_4 + 2] & 0xff);
			k = k << 8;
			k = k | (data[i_4 + 1] & 0xff);
			k = k << 8;
			k = k | (data[i_4 + 0] & 0xff);
			k *= m;
			k ^= k >>> r;
			k *= m;
			h *= m;
			h ^= k;
		}
		int len_m = len_4 << 2;
		int left = len - len_m;
		if (left != 0) {
			if (left >= 3) {
				h ^= (int) data[len - 3] << 16;
			}
			if (left >= 2) {
				h ^= (int) data[len - 2] << 8;
			}
			if (left >= 1) {
				h ^= (int) data[len - 1];
			}
			h *= m;
		}
		h ^= h >>> 13;
		h *= m;
		h ^= h >>> 15;
		return h;
	}
}