001/*******************************************************************************
002 * This software is provided as a supplement to the authors' textbooks on digital
003 * image processing published by Springer-Verlag in various languages and editions.
004 * Permission to use and distribute this software is granted under the BSD 2-Clause
005 * "Simplified" License (see http://opensource.org/licenses/BSD-2-Clause).
006 * Copyright (c) 2006-2023 Wilhelm Burger, Mark J. Burge. All rights reserved.
007 * Visit https://imagingbook.com for additional details.
008 ******************************************************************************/
009
010package imagingbook.common.noise.hashing;
011
012/**
013 * <p>
014 * Integer hash function proposed by Thomas Wang in [1]. See [2] for details.
015 * </p>
016 * <p>
017 * [1] Thomas Wang, "Integer Hash Function",
018 * <a href="http://web.archive.org/web/20071223173210/http://www.concentric.net/~Ttwang/tech/inthash.htm">
019 * http://www.concentric.net/~Ttwang/tech/inthash.htm</a> (Jan. 2007).<br> [2] W. Burger, M.J. Burge, <em>Principles of
020 * Digital Image Processing &ndash; Advanced Methods</em> (Vol. 3), Supplementary Chapter 8: "Synthetic Gradient Noise",
021 * Springer (2013). <a href=
022 * "https://dx.doi.org/10.13140/RG.2.1.3427.7284">https://dx.doi.org/10.13140/RG.2.1.3427.7284</a>
023 * </p>
024 *
025 * @author WB
026 * @version 2022/11/24
027 */
028public class Hash32ShiftMult extends Hash32 {
029        
030        /**
031         * Constructor, creates a hash function with a random seed value.
032         */
033        public Hash32ShiftMult() {
034                this(0);
035        }
036        
037        /**
038         * Constructor creating a hash function with the specified seed value.
039         * @param seed the random seed value (set to 0 use a random seed value).
040         */
041        public Hash32ShiftMult(int seed) {
042                super(seed);
043        }
044        
045        @Override
046        int hashInt(int key) {
047                key = key + seed;       // WB added
048                int c2 = 668265261; //=  0x27d4eb2d, which is not a prime, closest prime is 668265263
049                key = (key ^ 61) ^ (key >>> 16);
050                key = key + (key << 3);
051                key = key ^ (key >>> 4);
052                key = key * c2;
053                key = key ^ (key >>> 15);
054                return key;
055        }
056}