/**
*
* 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