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/*
 * 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.lucene.codecs.bloom;

import org.apache.lucene.util.BytesRef;

/**
 * This is a very fast, non-cryptographic hash suitable for general hash-based
 * lookup. See http://murmurhash.googlepages.com/ for more details.
 * 

* The C version of MurmurHash 2.0 found at that site was ported to Java by * Andrzej Bialecki (ab at getopt org). *

*

* 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. *

* @lucene.experimental */ public final class MurmurHash2 extends HashFunction{ 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 final int hash(BytesRef br) { return hash32(br.bytes, br.offset, br.length); } @Override public String toString() { return getClass().getSimpleName(); } }




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