001/**
002 * Copyright (c) 2012, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.openimaj.ml.sketch.bloom;
031
032import gnu.trove.map.hash.TIntIntHashMap;
033
034import org.openimaj.ml.sketch.SummarySketcher;
035import org.openimaj.util.hash.StringMurmurHashFunction;
036import org.openimaj.util.hash.StringMurmurHashFunctionFactory;
037
038/**
039 * The bloom sketch as described by
040 * http://lkozma.net/blog/sketching-data-structures/
041 * 
042 * @author Sina Samangooei (ss@ecs.soton.ac.uk)
043 * 
044 */
045public class Bloom implements SummarySketcher<String, Boolean> {
046
047        private StringMurmurHashFunction[] maps;
048        private TIntIntHashMap table;
049        private int nwords;
050
051        /**
052         * @param ntables
053         *            the number of hash functions
054         * @param nwords
055         *            the range of the hash functions
056         */
057        public Bloom(int ntables, int nwords) {
058                maps = new StringMurmurHashFunction[ntables];
059
060                final StringMurmurHashFunctionFactory fact = new StringMurmurHashFunctionFactory();
061                for (int i = 0; i < maps.length; i++) {
062                        maps[i] = fact.create();
063                }
064
065                this.nwords = nwords;
066                this.table = new TIntIntHashMap(nwords);
067        }
068
069        @Override
070        public void update(String data, Boolean value) {
071                for (final StringMurmurHashFunction map : maps) {
072                        final int hash = map.computeHashCode(data);
073                        final int loc = Math.abs(hash) % this.nwords;
074                        this.table.put(loc, 1);
075                }
076        }
077
078        @Override
079        public Boolean query(String data) {
080                boolean found = false;
081                for (final StringMurmurHashFunction map : maps) {
082                        final int hash = map.computeHashCode(data);
083                        final int loc = Math.abs(hash) % this.nwords;
084                        found = this.table.get(loc) == 1;
085                        if (found)
086                                return found;
087                }
088                return found;
089        }
090
091}