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* Copyright 2010 Red Hat Inc. and/or its affiliates and other
* contributors as indicated by the @author tags. All rights reserved.
* See the copyright.txt in the distribution for a full listing of
* individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
package org.infinispan.commons.hash;
import org.infinispan.marshall.Ids;
import org.infinispan.marshall.exts.NoStateExternalizer;
import org.infinispan.util.ByteArrayKey;
import org.infinispan.util.Util;
import java.io.ObjectInput;
import java.nio.charset.Charset;
import java.util.Set;
/**
* An implementation of Austin Appleby's MurmurHash2.0 algorithm, as documented on <a href="http://sites.google.com/site/murmurhash/">his website</a>.
* <p />
* This implementation is based on the slower, endian-neutral version of the algorithm as documented on the site,
* ported from Austin Appleby's original C++ version <a href="http://sites.google.com/site/murmurhash/MurmurHashNeutral2.cpp">MurmurHashNeutral2.cpp</a>.
* <p />
* Other implementations are documented on Wikipedia's <a href="http://en.wikipedia.org/wiki/MurmurHash">MurmurHash</a> page.
* <p />
* @see <a href="http://sites.google.com/site/murmurhash/">MurmurHash website</a>
* @see <a href="http://en.wikipedia.org/wiki/MurmurHash">MurmurHash entry on Wikipedia</a>
* @see MurmurHash2Compat
* @author Manik Surtani
* @version 4.1
*/
public class MurmurHash2 implements Hash {
private static final int M = 0x5bd1e995;
private static final int R = 24;
private static final int H = -1;
private static final Charset UTF8 = Charset.forName("UTF-8");
@Override
public final int hash(byte[] payload) {
int h = H;
int len = payload.length;
int offset = 0;
while (len >= 4) {
int k = payload[offset];
k |= payload[offset + 1] << 8;
k |= payload[offset + 2] << 16;
k |= payload[offset + 3] << 24;
k *= M;
k ^= k >>> R;
k *= M;
h *= M;
h ^= k;
len -= 4;
offset += 4;
}
switch (len) {
case 3:
h ^= payload[offset + 2] << 16;
case 2:
h ^= payload[offset + 1] << 8;
case 1:
h ^= payload[offset];
h *= M;
}
h ^= h >>> 13;
h *= M;
h ^= h >>> 15;
return h;
}
@Override
public final int hash(int hashcode) {
byte[] b = new byte[4];
b[0] = (byte) hashcode;
b[1] = (byte) (hashcode >>> 8);
b[2] = (byte) (hashcode >>> 16);
b[3] = (byte) (hashcode >>> 24);
return hash(b);
}
@Override
public final int hash(Object o) {
if (o instanceof byte[])
return hash((byte[]) o);
else if (o instanceof String)
return hash(((String) o).getBytes(UTF8));
else if (o instanceof ByteArrayKey)
return hash(((ByteArrayKey) o).getData());
else
return hash(o.hashCode());
}
public static class Externalizer extends NoStateExternalizer<MurmurHash2> {
@Override
public Set<Class<? extends MurmurHash2>> getTypeClasses() {
return Util.<Class<? extends MurmurHash2>>asSet(MurmurHash2.class);
}
@Override
public MurmurHash2 readObject(ObjectInput input) {
return new MurmurHash2();
}
@Override
public Integer getId() {
return Ids.MURMURHASH_2;
}
}
}