Java Hash Calculate hash()

Description

Optimized implementation of #hash(int[]) with 0 args.

License

BSD License

Declaration

public static int hash()

Method Source Code

//package com.java2s;
/*BEGIN_COPYRIGHT_BLOCK*
    //ww w . j a v a 2 s.co m
PLT Utilities BSD License
    
Copyright (c) 2007-2010 JavaPLT group at Rice University
All rights reserved.
    
Developed by:   Java Programming Languages Team
        Rice University
        http://www.cs.rice.edu/~javaplt/
    
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  and the following disclaimer.
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  conditions and the following disclaimer in the documentation and/or other materials provided 
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public class Main {
    /** Prime number used for hashing (approximately 2^32 divided by the golden ratio). */
    private static final int KNUTH_CONST = -1640531535;

    /** Optimized implementation of {@link #hash(int[])} with 0 args. */
    public static int hash() {
        return 1;
    }

    /** Optimized implementation of {@link #hash(int[])} with 1 arg. */
    public static int hash(int a) {
        return KNUTH_CONST ^ a;
    }

    /** Optimized implementation of {@link #hash(int[])}) with 2 args. */
    public static int hash(int a, int b) {
        return ((KNUTH_CONST ^ a) * KNUTH_CONST) ^ b;
    }

    /** Optimized implementation of {@link #hash(int[])} with 3 args. */
    public static int hash(int a, int b, int c) {
        return ((((KNUTH_CONST ^ a) * KNUTH_CONST) ^ b) * KNUTH_CONST) ^ c;
    }

    /** Optimized implementation of {@link #hash(int[])} with 4 args. */
    public static int hash(int a, int b, int c, int d) {
        return ((((((KNUTH_CONST ^ a) * KNUTH_CONST) ^ b) * KNUTH_CONST) ^ c) * KNUTH_CONST) ^ d;
    }

    /**
     * Produce a hash value based on the given keys according to an algorithm attributed to
     * Knuth (The Art of Programming, Vol. 3, Sorting and Searching) (TODO: verify this source).
     * The key idea is to combine 32-bit hash keys (where a typical class has multiple hash keys)
     * using exclusive OR after multiplying the existing accumulated result by a large prime number.
     */
    public static int hash(int... keys) {
        int len = keys.length;
        int result = 1;
        for (int i = 0; i < len; i++) {
            result = (result * KNUTH_CONST) ^ keys[i];
        }
        return result;
    }

    /** Optimized implementation of {@link #hash(Object[])} with 1 arg. */
    public static int hash(Object a) {
        return hash((a == null) ? 0 : a.hashCode());
    }

    /** Optimized implementation of {@link #hash(Object[])}) with 2 args. */
    public static int hash(Object a, Object b) {
        return hash((a == null) ? 0 : a.hashCode(), (b == null) ? 0 : b.hashCode());
    }

    /** Optimized implementation of {@link #hash(Object[])} with 3 args. */
    public static int hash(Object a, Object b, Object c) {
        return hash((a == null) ? 0 : a.hashCode(), (b == null) ? 0 : b.hashCode(), (c == null) ? 0 : c.hashCode());
    }

    /** Optimized implementation of {@link #hash(Object[])} with 4 args. */
    public static int hash(Object a, Object b, Object c, Object d) {
        return hash((a == null) ? 0 : a.hashCode(), (b == null) ? 0 : b.hashCode(), (c == null) ? 0 : c.hashCode(),
                (d == null) ? 0 : d.hashCode());
    }

    /** Produce a hash code for an object in which {@code #equals()} depends on the given values. */
    public static int hash(Object... objs) {
        int len = objs.length;
        int[] keys = new int[len];
        for (int i = 0; i < len; i++) {
            Object obj = objs[i];
            keys[i] = (obj == null) ? 0 : obj.hashCode();
        }
        return hash(keys);
    }

    /** Produce a hash code for an object in which {@code equals()} depends on the given values. */
    public static int hash(Iterable<?> iter) {
        int result = 1;
        for (Object obj : iter) {
            int key = (obj == null) ? 0 : obj.hashCode();
            result = (result * KNUTH_CONST) ^ key;
        }
        return result;
    }
}

Java Hash Calculate hash()

Description

License

Declaration

Method Source Code

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