    001    /**
    002     *
    003     * Copyright (c) 2005, European Commission project OneLab under contract 034819
    004     * (http://www.one-lab.org)
    005     *
    006     * All rights reserved.
    007     * Redistribution and use in source and binary forms, with or
    008     * without modification, are permitted provided that the following
    009     * conditions are met:
    010     *  - Redistributions of source code must retain the above copyright
    011     *    notice, this list of conditions and the following disclaimer.
    012     *  - Redistributions in binary form must reproduce the above copyright
    013     *    notice, this list of conditions and the following disclaimer in
    014     *    the documentation and/or other materials provided with the distribution.
    015     *  - Neither the name of the University Catholique de Louvain - UCL
    016     *    nor the names of its contributors may be used to endorse or
    017     *    promote products derived from this software without specific prior
    018     *    written permission.
    019     *
    020     * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    021     * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    022     * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
    023     * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    024     * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
    025     * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
    026     * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
    027     * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
    028     * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    029     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
    030     * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    031     * POSSIBILITY OF SUCH DAMAGE.
    032     */
    033
    034    /**
    035     * Licensed to the Apache Software Foundation (ASF) under one
    036     * or more contributor license agreements.  See the NOTICE file
    037     * distributed with this work for additional information
    038     * regarding copyright ownership.  The ASF licenses this file
    039     * to you under the Apache License, Version 2.0 (the
    040     * "License"); you may not use this file except in compliance
    041     * with the License.  You may obtain a copy of the License at
    042     *
    043     *     http://www.apache.org/licenses/LICENSE-2.0
    044     *
    045     * Unless required by applicable law or agreed to in writing, software
    046     * distributed under the License is distributed on an "AS IS" BASIS,
    047     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    048     * See the License for the specific language governing permissions and
    049     * limitations under the License.
    050     */
    051    package org.apache.hadoop.util.bloom;
    052
    053    import org.apache.hadoop.classification.InterfaceAudience;
    054    import org.apache.hadoop.classification.InterfaceStability;
    055    import org.apache.hadoop.util.hash.Hash;
    056
    057    /**
    058     * Implements a hash object that returns a certain number of hashed values.
    059     *
    060     * @see Key The general behavior of a key being stored in a filter
    061     * @see Filter The general behavior of a filter
    062     */
    063    @InterfaceAudience.Public
    064    @InterfaceStability.Stable
    065    public final class HashFunction {
    066      /** The number of hashed values. */
    067      private int nbHash;
    068
    069      /** The maximum highest returned value. */
    070      private int maxValue;
    071
    072      /** Hashing algorithm to use. */
    073      private Hash hashFunction;
    074
    075      /**
    076       * Constructor.
    077       * <p>
    078       * Builds a hash function that must obey to a given maximum number of returned values and a highest value.
    079       * @param maxValue The maximum highest returned value.
    080       * @param nbHash The number of resulting hashed values.
    081       * @param hashType type of the hashing function (see {@link Hash}).
    082       */
    083      public HashFunction(int maxValue, int nbHash, int hashType) {
    084        if (maxValue <= 0) {
    085          throw new IllegalArgumentException("maxValue must be > 0");
    086        }
    087
    088        if (nbHash <= 0) {
    089          throw new IllegalArgumentException("nbHash must be > 0");
    090        }
    091
    092        this.maxValue = maxValue;
    093        this.nbHash = nbHash;
    094        this.hashFunction = Hash.getInstance(hashType);
    095        if (this.hashFunction == null)
    096          throw new IllegalArgumentException("hashType must be known");
    097      }
    098
    099      /** Clears <i>this</i> hash function. A NOOP */
    100      public void clear() {
    101      }
    102
    103      /**
    104       * Hashes a specified key into several integers.
    105       * @param k The specified key.
    106       * @return The array of hashed values.
    107       */
    108      public int[] hash(Key k){
    109          byte[] b = k.getBytes();
    110          if (b == null) {
    111            throw new NullPointerException("buffer reference is null");
    112          }
    113          if (b.length == 0) {
    114            throw new IllegalArgumentException("key length must be > 0");
    115          }
    116          int[] result = new int[nbHash];
    117          for (int i = 0, initval = 0; i < nbHash; i++) {
    118              initval = hashFunction.hash(b, initval);
    119              result[i] = Math.abs(initval % maxValue);
    120          }
    121          return result;
    122      }
    123    }