org.apache.datasketches.hash.XxHash Maven / Gradle / Ivy
/*
* 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.datasketches.hash;
import org.apache.datasketches.memory.Memory;
/**
* The XxHash is a fast, non-cryptographic, 64-bit hash function that has
* excellent avalanche and 2-way bit independence properties.
* This java version used the C++ version and the OpenHFT/Zero-Allocation-Hashing implementation
* referenced below as inspiration.
*
* The C++ source repository:
*
* https://github.com/Cyan4973/xxHash. It has a BSD 2-Clause License:
*
* http://www.opensource.org/licenses/bsd-license.php See LICENSE.
*
*
Portions of this code were adapted from
*
* OpenHFT/Zero-Allocation-Hashing, which has an Apache 2 license as does this site. See LICENSE.
*
* @author Lee Rhodes
*/
public class XxHash {
// Unsigned, 64-bit primes
private static final long P1 = -7046029288634856825L;
private static final long P2 = -4417276706812531889L;
private static final long P3 = 1609587929392839161L;
private static final long P4 = -8796714831421723037L;
private static final long P5 = 2870177450012600261L;
/**
* Compute the hash of the given Memory object.
* @param mem The given Memory object
* @param offsetBytes Starting at this offset in bytes
* @param lengthBytes Continuing for this number of bytes
* @param seed use this seed for the hash function
* @return return the resulting 64-bit hash value.
*/
public static long hash(final Memory mem, final long offsetBytes, final long lengthBytes,
final long seed) {
return mem.xxHash64(offsetBytes, lengthBytes, seed);
}
/**
* Returns a 64-bit hash.
* @param in a long
* @param seed A long valued seed.
* @return the hash
*/
public static long hash(final long in, final long seed) {
long hash = seed + P5;
hash += 8;
long k1 = in;
k1 *= P2;
k1 = Long.rotateLeft(k1, 31);
k1 *= P1;
hash ^= k1;
hash = (Long.rotateLeft(hash, 27) * P1) + P4;
return finalize(hash);
}
private static long finalize(long hash) {
hash ^= hash >>> 33;
hash *= P2;
hash ^= hash >>> 29;
hash *= P3;
hash ^= hash >>> 32;
return hash;
}
}