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 * Hash function proposed by G Ward in [1]. See [2] for details.
015 * </p>
016 * <p>
017 * [1] G. Ward, "A recursive implementation of the Perlin noise function", Graphics Gems II (1991).<br> [2] W. Burger,
018 * M.J. Burge, <em>Principles of Digital Image Processing &ndash; Advanced Methods</em> (Vol. 3), Supplementary Chapter
019 * 8: "Synthetic Gradient Noise", Springer (2013). <a href=
020 * "https://dx.doi.org/10.13140/RG.2.1.3427.7284">https://dx.doi.org/10.13140/RG.2.1.3427.7284</a>
021 * </p>
022 *
023 * @author WB
024 * @version 2022/11/24
025 */
026public class Hash32Ward extends Hash32 {
027        
028        /**
029         * Constructor, creates a hash function with a random seed value.
030         */
031        public Hash32Ward() {
032                this(0);
033        }
034        
035        /**
036         * Constructor creating a hash function with the specified seed value.
037         * @param seed the random seed value (set to 0 use a random seed value).
038         */
039        public Hash32Ward(int seed) {
040                super(seed);
041        }
042        
043        @Override
044        int hashInt(int key) {
045                key = key + seed;       // WB added
046                // lower 16 bits are highly repetitive and "perfectly" uniform!
047                key = (key << 13) ^ key; // ^ denotes bitwise XOR operation
048                key = (key * (key * key * 15731 + 789221) + 1376312589);
049                return key;
050        }
051        
052        public static void main(String[] args) {
053                Hash32Ward hf = new Hash32Ward();
054                for (int k = 0; k < 256; k++) {
055                        System.out.format("%d : %10f\n", k, hf.hash(k));
056                        
057                }
058        }
059}