| /** |
| * |
| * 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 |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
| * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, |
| * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, |
| * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; |
| * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER |
| * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN |
| * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| * POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| /** |
| * 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 java.io.DataInput; |
| import java.io.DataOutput; |
| import java.io.IOException; |
| |
| import java.util.BitSet; |
| |
| /** |
| * Implements a <i>Bloom filter</i>, as defined by Bloom in 1970. |
| * <p> |
| * The Bloom filter is a data structure that was introduced in 1970 and that has been adopted by |
| * the networking research community in the past decade thanks to the bandwidth efficiencies that it |
| * offers for the transmission of set membership information between networked hosts. A sender encodes |
| * the information into a bit vector, the Bloom filter, that is more compact than a conventional |
| * representation. Computation and space costs for construction are linear in the number of elements. |
| * The receiver uses the filter to test whether various elements are members of the set. Though the |
| * filter will occasionally return a false positive, it will never return a false negative. When creating |
| * the filter, the sender can choose its desired point in a trade-off between the false positive rate and the size. |
| * |
| * <p> |
| * Originally created by |
| * <a href="http://www.one-lab.org">European Commission One-Lab Project 034819</a>. |
| * |
| * @see Filter The general behavior of a filter |
| * |
| * @see <a href="http://portal.acm.org/citation.cfm?id=362692&dl=ACM&coll=portal">Space/Time Trade-Offs in Hash Coding with Allowable Errors</a> |
| */ |
| public class BloomFilter extends Filter { |
| private static final byte[] bitvalues = new byte[] { |
| (byte)0x01, |
| (byte)0x02, |
| (byte)0x04, |
| (byte)0x08, |
| (byte)0x10, |
| (byte)0x20, |
| (byte)0x40, |
| (byte)0x80 |
| }; |
| |
| /** The bit vector. */ |
| BitSet bits; |
| |
| /** Default constructor - use with readFields */ |
| public BloomFilter() { |
| super(); |
| } |
| |
| /** |
| * Constructor |
| * @param vectorSize The vector size of <i>this</i> filter. |
| * @param nbHash The number of hash function to consider. |
| * @param hashType type of the hashing function (see |
| * {@link org.apache.hadoop.util.hash.Hash}). |
| */ |
| public BloomFilter(int vectorSize, int nbHash, int hashType) { |
| super(vectorSize, nbHash, hashType); |
| |
| bits = new BitSet(this.vectorSize); |
| } |
| |
| @Override |
| public void add(Key key) { |
| if(key == null) { |
| throw new NullPointerException("key cannot be null"); |
| } |
| |
| int[] h = hash.hash(key); |
| hash.clear(); |
| |
| for(int i = 0; i < nbHash; i++) { |
| bits.set(h[i]); |
| } |
| } |
| |
| @Override |
| public void and(Filter filter) { |
| if(filter == null |
| || !(filter instanceof BloomFilter) |
| || filter.vectorSize != this.vectorSize |
| || filter.nbHash != this.nbHash) { |
| throw new IllegalArgumentException("filters cannot be and-ed"); |
| } |
| |
| this.bits.and(((BloomFilter) filter).bits); |
| } |
| |
| @Override |
| public boolean membershipTest(Key key) { |
| if(key == null) { |
| throw new NullPointerException("key cannot be null"); |
| } |
| |
| int[] h = hash.hash(key); |
| hash.clear(); |
| for(int i = 0; i < nbHash; i++) { |
| if(!bits.get(h[i])) { |
| return false; |
| } |
| } |
| return true; |
| } |
| |
| @Override |
| public void not() { |
| bits.flip(0, vectorSize - 1); |
| } |
| |
| @Override |
| public void or(Filter filter) { |
| if(filter == null |
| || !(filter instanceof BloomFilter) |
| || filter.vectorSize != this.vectorSize |
| || filter.nbHash != this.nbHash) { |
| throw new IllegalArgumentException("filters cannot be or-ed"); |
| } |
| bits.or(((BloomFilter) filter).bits); |
| } |
| |
| @Override |
| public void xor(Filter filter) { |
| if(filter == null |
| || !(filter instanceof BloomFilter) |
| || filter.vectorSize != this.vectorSize |
| || filter.nbHash != this.nbHash) { |
| throw new IllegalArgumentException("filters cannot be xor-ed"); |
| } |
| bits.xor(((BloomFilter) filter).bits); |
| } |
| |
| @Override |
| public String toString() { |
| return bits.toString(); |
| } |
| |
| /** |
| * @return size of the the bloomfilter |
| */ |
| public int getVectorSize() { |
| return this.vectorSize; |
| } |
| |
| // Writable |
| |
| @Override |
| public void write(DataOutput out) throws IOException { |
| super.write(out); |
| byte[] bytes = new byte[getNBytes()]; |
| for(int i = 0, byteIndex = 0, bitIndex = 0; i < vectorSize; i++, bitIndex++) { |
| if (bitIndex == 8) { |
| bitIndex = 0; |
| byteIndex++; |
| } |
| if (bitIndex == 0) { |
| bytes[byteIndex] = 0; |
| } |
| if (bits.get(i)) { |
| bytes[byteIndex] |= bitvalues[bitIndex]; |
| } |
| } |
| out.write(bytes); |
| } |
| |
| @Override |
| public void readFields(DataInput in) throws IOException { |
| super.readFields(in); |
| bits = new BitSet(this.vectorSize); |
| byte[] bytes = new byte[getNBytes()]; |
| in.readFully(bytes); |
| for(int i = 0, byteIndex = 0, bitIndex = 0; i < vectorSize; i++, bitIndex++) { |
| if (bitIndex == 8) { |
| bitIndex = 0; |
| byteIndex++; |
| } |
| if ((bytes[byteIndex] & bitvalues[bitIndex]) != 0) { |
| bits.set(i); |
| } |
| } |
| } |
| |
| /* @return number of bytes needed to hold bit vector */ |
| private int getNBytes() { |
| return (vectorSize + 7) / 8; |
| } |
| }//end class |