Android Hash Code Calculate hashCode(int x)

Description

hash Code

License

Apache License

Declaration

public static int hashCode(int x) 

Method Source Code

//package com.java2s;
/*/* www  .  ja  v  a  2s  .  c o  m*/
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

public class Main {
    /**
     * Hash every element uniformly using the Modified Bernstein hash.
     *
     * <p>Useful to implement a {@link Object#hashCode} for uniformly distributed data.</p>
     *
     * @param array a non-{@code null} array of integers
     *
     * @return the numeric hash code
     */
    public static int hashCode(int[] array) {
        if (array == null) {
            return 0;
        }

        /*
         *  Note that we use 31 here instead of 33 since it's preferred in Effective Java
         *  and used elsewhere in the runtime (e.g. Arrays#hashCode)
         *
         *  That being said 33 and 31 are nearly identical in terms of their usefulness
         *  according to http://svn.apache.org/repos/asf/apr/apr/trunk/tables/apr_hash.c
         */
        int h = 1;
        for (int x : array) {
            // Strength reduction; in case the compiler has illusions about divisions being faster
            h = ((h << 5) - h) ^ x; // (h * 31) XOR x
        }

        return h;
    }

    /**
     * Hash every element uniformly using the Modified Bernstein hash.
     *
     * <p>Useful to implement a {@link Object#hashCode} for uniformly distributed data.</p>
     *
     * @param array a non-{@code null} array of floats
     *
     * @return the numeric hash code
     */
    public static int hashCode(float[] array) {
        if (array == null) {
            return 0;
        }

        int h = 1;
        for (float f : array) {
            int x = Float.floatToIntBits(f);
            h = ((h << 5) - h) ^ x; // (h * 31) XOR x
        }

        return h;
    }

    /**
     * Hash every element uniformly using the Modified Bernstein hash.
     *
     * <p>Useful to implement a {@link Object#hashCode} for uniformly distributed data.</p>
     *
     * @param array a non-{@code null} array of objects
     *
     * @return the numeric hash code
     */
    public static <T> int hashCode(T[] array) {
        if (array == null) {
            return 0;
        }

        int h = 1;
        for (T o : array) {
            int x = (o == null) ? 0 : o.hashCode();
            h = ((h << 5) - h) ^ x; // (h * 31) XOR x
        }

        return h;
    }

    public static <T> int hashCode(T a) {
        return (a == null) ? 0 : a.hashCode();
    }

    public static <T> int hashCode(T a, T b) {
        int h = hashCode(a);

        int x = (b == null) ? 0 : b.hashCode();
        h = ((h << 5) - h) ^ x; // (h * 31) XOR x

        return h;
    }

    public static <T> int hashCode(T a, T b, T c) {
        int h = hashCode(a, b);

        int x = (c == null) ? 0 : c.hashCode();
        h = ((h << 5) - h) ^ x; // (h * 31) XOR x

        return h;
    }

    public static <T> int hashCode(T a, T b, T c, T d) {
        int h = hashCode(a, b, c);

        int x = (d == null) ? 0 : d.hashCode();
        h = ((h << 5) - h) ^ x; // (h * 31) XOR x

        return h;
    }

    public static int hashCode(int x) {
        return hashCode(new int[] { x });
    }

    public static int hashCode(int x, int y) {
        return hashCode(new int[] { x, y });
    }

    public static int hashCode(int x, int y, int z) {
        return hashCode(new int[] { x, y, z });
    }

    public static int hashCode(int x, int y, int z, int w) {
        return hashCode(new int[] { x, y, z, w });
    }

    public static int hashCode(int x, int y, int z, int w, int t) {
        return hashCode(new int[] { x, y, z, w, t });
    }
}

Related

1. hashCode(T a, T b)
2. hashCode(T a, T b, T c)
3. hashCode(T a, T b, T c, T d)
4. hashCode(T[] array)
5. hashCode(float[] array)
6. hashCode(int x, int y)
7. hashCode(int x, int y, int z)
8. hashCode(int x, int y, int z, int w)
9. hashCode(int x, int y, int z, int w, int t)