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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.hadoop.hbase.util;

import org.apache.yetus.audience.InterfaceAudience;
import org.apache.yetus.audience.InterfaceStability;

/**
 * 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).

*/ @InterfaceAudience.Private @InterfaceStability.Stable public class MurmurHash extends Hash { private static MurmurHash _instance = new MurmurHash(); public static Hash getInstance() { return _instance; } @Override public int hash(HashKey hashKey, int seed) { int m = 0x5bd1e995; int r = 24; int length = hashKey.length(); int h = seed ^ length; int len_4 = length >> 2; for (int i = 0; i < len_4; i++) { int i_4 = (i << 2); int k = hashKey.get(i_4 + 3); k = k << 8; k = k | (hashKey.get(i_4 + 2) & 0xff); k = k << 8; k = k | (hashKey.get(i_4 + 1) & 0xff); k = k << 8; // noinspection PointlessArithmeticExpression k = k | (hashKey.get(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; int i_m = len_m; if (left != 0) { if (left >= 3) { h ^= hashKey.get(i_m + 2) << 16; } if (left >= 2) { h ^= hashKey.get(i_m + 1) << 8; } if (left >= 1) { h ^= hashKey.get(i_m); } h *= m; } h ^= h >>> 13; h *= m; h ^= h >>> 15; return h; } }




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