org.apache.jackrabbit.oak.util.SipHash 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.jackrabbit.oak.util;
/**
* An implementation of the SipHash-2-2 function, to prevent hash flooding.
*/
public class SipHash {
private final long v0, v1, v2, v3;
public SipHash(long seed) {
long k0 = seed;
long k1 = Long.rotateLeft(seed, 32);
v0 = k0 ^ 0x736f6d6570736575L;
v1 = k1 ^ 0x646f72616e646f6dL;
v2 = k0 ^ 0x6c7967656e657261L;
v3 = k1 ^ 0x7465646279746573L;
}
public SipHash(SipHash parent, long m) {
long v0 = parent.v0;
long v1 = parent.v1;
long v2 = parent.v2;
long v3 = parent.v3;
int repeat = 2;
for (int i = 0; i < repeat; i++) {
v0 += v1;
v2 += v3;
v1 = Long.rotateLeft(v1, 13);
v3 = Long.rotateLeft(v3, 16);
v1 ^= v0;
v3 ^= v2;
v0 = Long.rotateLeft(v0, 32);
v2 += v1;
v0 += v3;
v1 = Long.rotateLeft(v1, 17);
v3 = Long.rotateLeft(v3, 21);
v1 ^= v2;
v3 ^= v0;
v2 = Long.rotateLeft(v2, 32);
}
v0 ^= m;
this.v0 = v0;
this.v1 = v1;
this.v2 = v2;
this.v3= v3;
}
@Override
public int hashCode() {
long x = v0 ^ v1 ^ v2 ^ v3;
return (int) (x ^ (x >>> 16));
}
}