| /* |
| * 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.solr.common.util; |
| |
| /** |
| * 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> |
| * <p> |
| * The code from getopt.org was adapted by Mark Harwood in the form here as one of a pluggable choice of |
| * hashing functions as the core function had to be adapted to work with BytesRefs with offsets and lengths |
| * rather than raw byte arrays. |
| * </p> |
| * @lucene.experimental |
| */ |
| public final class MurmurHash2 { |
| |
| public static final MurmurHash2 INSTANCE = new MurmurHash2(); |
| |
| private MurmurHash2() {} |
| |
| public static int hash(byte[] data, int seed, int offset, int len) { |
| int m = 0x5bd1e995; |
| int r = 24; |
| int h = seed ^ len; |
| int len_4 = len >> 2; |
| for (int i = 0; i < len_4; i++) { |
| int i_4 = offset + (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 ^= data[offset + len - 3] << 16; |
| } |
| if (left >= 2) { |
| h ^= data[offset + len - 2] << 8; |
| } |
| if (left >= 1) { |
| h ^= data[offset + len - 1]; |
| } |
| h *= m; |
| } |
| h ^= h >>> 13; |
| h *= m; |
| h ^= h >>> 15; |
| return h; |
| } |
| |
| /** |
| * Generates 32 bit hash from byte array with default seed value. |
| * |
| * @param data |
| * byte array to hash |
| * @param offset |
| * the start position in the array to hash |
| * @param len |
| * length of the array elements to hash |
| * @return 32 bit hash of the given array |
| */ |
| public static final int hash32(final byte[] data, int offset, int len) { |
| return MurmurHash2.hash(data, 0x9747b28c, offset, len); |
| } |
| |
| |
| @Override |
| public String toString() { |
| return getClass().getSimpleName(); |
| } |
| } |