it.uniroma3.mat.extendedset.utilities.IntHashCode Maven / Gradle / Ivy
/*
* (c) 2010 Alessandro Colantonio
*
*
*
* 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 it.uniroma3.mat.extendedset.utilities;
/**
* Hash functions for integers and integer arrays.
*
* @author Alessandro Colantonio
* @version $Id: IntHashCode.java 127 2010-12-21 20:22:12Z cocciasik $
*/
public class IntHashCode {
/**
* Computes a hashcode for an integer
*
* Inspired by Thomas Wang's function, described at http://www.concentric.net/~ttwang/tech/inthash.htm
*
* @param key
* the given integer
* @return the hashcode
*/
public static int hashCode(int key) {
key = ~key + (key << 15);
key ^= key >>> 12;
key += key << 2;
key ^= key >>> 4;
key *= 2057;
key ^= key >>> 16;
return key;
}
/**
* Computes the hashcode of an array of integers
*
* @param keys
* the given integer array
* @return the hashcode
*/
public static int hashCode(int[] keys) {
return hashCode(keys, keys.length, 0);
}
/**
* Computes the hashcode of an array of integers
*
* It is based on MurmurHash3 Algorithm, described at http://sites.google.com/site/murmurhash
*
* @param keys
* the given integer array
* @param len
* number of elements to include, that is
* len <= keys.length
* @param seed
* initial seed
* @return the hashcode
*/
public static int hashCode(int[] keys, int len, int seed) {
int h = 0x971e137b ^ seed;
int c1 = 0x95543787;
int c2 = 0x2ad7eb25;
for (int i = 0; i < len; i++) {
int k = keys[i];
k *= c1;
k = (k << 11) | (k >>> 21); // rotl k, 11
k *= c2;
h ^= k;
h = (h << 2) - h + 0x52dce729;
c1 = (c1 << 2) + c1 + 0x7b7d159c;
c2 = (c2 << 2) + c2 + 0x6bce6396;
}
h ^= len;
h ^= h >>> 16;
h *= 0x85ebca6b;
h ^= h >>> 13;
h *= 0xc2b2ae35;
h ^= h >>> 16;
return h;
}
}