org.apache.hadoop.util.bloom.HashFunction Maven / Gradle / Ivy
/**
*
* Copyright (c) 2005, European Commission project OneLab under contract 034819
* (http://www.one-lab.org)
*
* All rights reserved.
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the distribution.
* - Neither the name of the University Catholique de Louvain - UCL
* nor the names of its contributors may be used to endorse or
* promote products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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/**
* 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.hadoop.util.bloom;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.util.hash.Hash;
/**
* Implements a hash object that returns a certain number of hashed values.
*
* @see Key The general behavior of a key being stored in a filter
* @see Filter The general behavior of a filter
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public final class HashFunction {
/** The number of hashed values. */
private int nbHash;
/** The maximum highest returned value. */
private int maxValue;
/** Hashing algorithm to use. */
private Hash hashFunction;
/**
* Constructor.
*
* Builds a hash function that must obey to a given maximum number of returned values and a highest value.
* @param maxValue The maximum highest returned value.
* @param nbHash The number of resulting hashed values.
* @param hashType type of the hashing function (see {@link Hash}).
*/
public HashFunction(int maxValue, int nbHash, int hashType) {
if (maxValue <= 0) {
throw new IllegalArgumentException("maxValue must be > 0");
}
if (nbHash <= 0) {
throw new IllegalArgumentException("nbHash must be > 0");
}
this.maxValue = maxValue;
this.nbHash = nbHash;
this.hashFunction = Hash.getInstance(hashType);
if (this.hashFunction == null)
throw new IllegalArgumentException("hashType must be known");
}
/** Clears this hash function. A NOOP */
public void clear() {
}
/**
* Hashes a specified key into several integers.
* @param k The specified key.
* @return The array of hashed values.
*/
public int[] hash(Key k){
byte[] b = k.getBytes();
if (b == null) {
throw new NullPointerException("buffer reference is null");
}
if (b.length == 0) {
throw new IllegalArgumentException("key length must be > 0");
}
int[] result = new int[nbHash];
for (int i = 0, initval = 0; i < nbHash; i++) {
initval = hashFunction.hash(b, initval);
result[i] = Math.abs(initval % maxValue);
}
return result;
}
}