Mega Code Archive
This is a very fast, non-cryptographic hash suitable for general hash-based lookup
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/*
* Copyright 2008-2010 the T2 Project ant the Others.
*
* Licensed 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.t2framework.commons.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>
*
* This is suitable for 32bit application, if 64bit we need to improve it.
*
* @see http://murmurhash.googlepages.com/
*/
public class MurmurHashFunction extends AbstractHashFunction {
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;
}
}
abstract class AbstractHashFunction implements HashFunction {
public int hash(byte[] bytes, int initval) {
return hash(bytes, bytes.length, initval);
}
public int hash(byte[] bytes) {
return hash(bytes, bytes.length, -1);
}
}
interface HashFunction {
int hash(byte[] bytes);
int hash(byte[] bytes, int initval);
int hash(byte[] bytes, int length, int initval);
}
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