001/**
002 * Copyright (c) 2011, 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.lsh.composition;
031
032import java.util.List;
033
034import org.openimaj.util.hash.HashFunction;
035import org.openimaj.util.hash.HashFunctionFactory;
036import org.openimaj.util.hash.composition.HashComposition;
037
038/**
039 * {@link HashComposition} that uses a polynomial function to combine the
040 * individual hashes. Based on the composition in the <a
041 * href="https://code.google.com/p/caltech-image-search/">Caltech Large Scale
042 * Image Search Toolbox</a>.
043 *
044 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
045 *
046 * @param <OBJECT>
047 *            Object being hashed
048 */
049public class PolyHashComposition<OBJECT> extends HashComposition<OBJECT> {
050        private static final int HASH_POLY = 1368547;
051        private static final int HASH_POLY_REM = 573440;
052        private static final int HASH_POLY_A[] =
053        { 1342, 876454, 656565, 223, 337, 9847, 87676, 34234, 23445, 76543, 8676234, 3497, 9876, 87856, 2342858 };
054
055        /**
056         * Construct with the given functions.
057         *
058         * @param functions
059         *            the underlying hash functions.
060         */
061        public PolyHashComposition(List<HashFunction<OBJECT>> functions) {
062                super(functions);
063        }
064
065        /**
066         * Construct with the given functions.
067         *
068         * @param first
069         *            the first function
070         * @param remainder
071         *            the remainder of the functions
072         */
073        @SafeVarargs
074        public PolyHashComposition(HashFunction<OBJECT> first, HashFunction<OBJECT>... remainder) {
075                super(first, remainder);
076        }
077
078        /**
079         * Construct with the factory which is used to produce the required number
080         * of functions.
081         *
082         * @param factory
083         *            the factory to use to produce the underlying hash functions.
084         * @param nFuncs
085         *            the number of functions to create for the composition
086         */
087        public PolyHashComposition(HashFunctionFactory<OBJECT> factory, int nFuncs) {
088                super(factory, nFuncs);
089        }
090
091        private final int addId(int id, int val, int pos) {
092                return (val * HASH_POLY_A[pos % HASH_POLY_A.length] % HASH_POLY) + (id * HASH_POLY_REM % HASH_POLY);
093        }
094
095        @Override
096        public int computeHashCode(OBJECT object) {
097                if (hashFunctions == null || hashFunctions.size() == 0)
098                        return 0;
099
100                int id = hashFunctions.get(0).computeHashCode(object);
101                for (int i = 1, s = hashFunctions.size(); i < s; i++) {
102                        final int val = hashFunctions.get(i).computeHashCode(object);
103
104                        id = addId(id, val, i);
105                }
106                return id;
107        }
108}