/*
* 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.mahout.math;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
/**
* This is a very fast, non-cryptographic hash suitable for general hash-based
* lookup. See http://murmurhash.googlepages.com/ for more details.
* <p/>
* <p>The C version of MurmurHash 2.0 found at that site was ported
* to Java by Andrzej Bialecki (ab at getopt org).</p>
*/
public final class MurmurHash {
private MurmurHash() {
}
/**
* Hashes bytes in an array.
* @param data The bytes to hash.
* @param seed The seed for the hash.
* @return The 32 bit hash of the bytes in question.
*/
public static int hash(byte[] data, int seed) {
return hash(ByteBuffer.wrap(data), seed);
}
/**
* Hashes bytes in part of an array.
* @param data The data to hash.
* @param offset Where to start munging.
* @param length How many bytes to process.
* @param seed The seed to start with.
* @return The 32-bit hash of the data in question.
*/
public static int hash(byte[] data, int offset, int length, int seed) {
return hash(ByteBuffer.wrap(data, offset, length), seed);
}
/**
* Hashes the bytes in a buffer from the current position to the limit.
* @param buf The bytes to hash.
* @param seed The seed for the hash.
* @return The 32 bit murmur hash of the bytes in the buffer.
*/
public static int hash(ByteBuffer buf, int seed) {
// save byte order for later restoration
ByteOrder byteOrder = buf.order();
buf.order(ByteOrder.LITTLE_ENDIAN);
int m = 0x5bd1e995;
int r = 24;
int h = seed ^ buf.remaining();
while (buf.remaining() >= 4) {
int k = buf.getInt();
k *= m;
k ^= k >>> r;
k *= m;
h *= m;
h ^= k;
}
if (buf.remaining() > 0) {
ByteBuffer finish = ByteBuffer.allocate(4).order(ByteOrder.LITTLE_ENDIAN);
// for big-endian version, use this first:
// finish.position(4-buf.remaining());
finish.put(buf).rewind();
h ^= finish.getInt();
h *= m;
}
h ^= h >>> 13;
h *= m;
h ^= h >>> 15;
buf.order(byteOrder);
return h;
}
public static long hash64A(byte[] data, int seed) {
return hash64A(ByteBuffer.wrap(data), seed);
}
public static long hash64A(byte[] data, int offset, int length, int seed) {
return hash64A(ByteBuffer.wrap(data, offset, length), seed);
}
public static long hash64A(ByteBuffer buf, int seed) {
ByteOrder byteOrder = buf.order();
buf.order(ByteOrder.LITTLE_ENDIAN);
long m = 0xc6a4a7935bd1e995L;
int r = 47;
long h = seed ^ (buf.remaining() * m);
while (buf.remaining() >= 8) {
long k = buf.getLong();
k *= m;
k ^= k >>> r;
k *= m;
h ^= k;
h *= m;
}
if (buf.remaining() > 0) {
ByteBuffer finish = ByteBuffer.allocate(8).order(ByteOrder.LITTLE_ENDIAN);
// for big-endian version, do this first:
// finish.position(8-buf.remaining());
finish.put(buf).rewind();
h ^= finish.getLong();
h *= m;
}
h ^= h >>> r;
h *= m;
h ^= h >>> r;
buf.order(byteOrder);
return h;
}
}