| /* |
| * 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.pig.impl.bloom; |
| |
| import org.apache.hadoop.util.bloom.Key; |
| |
| public class HashFunction { |
| /** The number of hashed values. */ |
| protected int nbHash; |
| /** The maximum highest returned value. */ |
| protected int maxValue; |
| /** Hashing algorithm to use. */ |
| protected Hash hashAlgorithm; |
| /** |
| * Constructor. |
| * <p> |
| * 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 hashAlgorithm type of the hashing algorithm (see {@link Hash}). |
| */ |
| public HashFunction(int maxValue, int nbHash, int hashAlgorithm) { |
| 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.hashAlgorithm = Hash.getInstance(hashAlgorithm); |
| } |
| |
| /** Clears <i>this</i> 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"); |
| } |
| return hashAlgorithm.hash(b, maxValue, nbHash); |
| } |
| } |