| /** |
| * 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.hadoop.util.hash; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| |
| /** |
| * 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> |
| */ |
| @InterfaceAudience.Private |
| @InterfaceStability.Unstable |
| public class MurmurHash extends Hash { |
| private static MurmurHash _instance = new MurmurHash(); |
| |
| public static Hash getInstance() { |
| return _instance; |
| } |
| |
| @Override |
| public int hash(byte[] data, int length, int seed) { |
| int m = 0x5bd1e995; |
| int r = 24; |
| |
| int h = seed ^ length; |
| |
| int len_4 = length >> 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; |
| } |
| |
| // avoid calculating modulo |
| int len_m = len_4 << 2; |
| int left = length - len_m; |
| |
| if (left != 0) { |
| if (left >= 3) { |
| h ^= (int) data[length - 3] << 16; |
| } |
| if (left >= 2) { |
| h ^= (int) data[length - 2] << 8; |
| } |
| if (left >= 1) { |
| h ^= (int) data[length - 1]; |
| } |
| |
| h *= m; |
| } |
| |
| h ^= h >>> 13; |
| h *= m; |
| h ^= h >>> 15; |
| |
| return h; |
| } |
| } |