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The Trove library provides high speed regular and primitive collections for Java.

There is a newer version: 3.0.3

// Copyright (c) 1999 CERN - European Organization for Nuclear Research.

// Permission to use, copy, modify, distribute and sell this software and
// its documentation for any purpose is hereby granted without fee,
// provided that the above copyright notice appear in all copies and that
// both that copyright notice and this permission notice appear in
// supporting documentation. CERN makes no representations about the
// suitability of this software for any purpose. It is provided "as is"
// without expressed or implied warranty.

package gnu.trove.impl;

/**
 * Provides various hash functions.
 *
 * @author [email protected]
 * @version 1.0, 09/24/99
 */
public final class HashFunctions {
    /**
     * Returns a hashcode for the specified value.
     *
     * @return  a hash code value for the specified value.
     */
    public static int hash(double value) {
        assert !Double.isNaN(value) : "Values of NaN are not supported.";

        long bits = Double.doubleToLongBits(value);
        return (int)(bits ^ (bits >>> 32));
        //return (int) Double.doubleToLongBits(value*663608941.737);
        //this avoids excessive hashCollisions in the case values are
        //of the form (1.0, 2.0, 3.0, ...)
    }

    /**
     * Returns a hashcode for the specified value.
     *
     * @return  a hash code value for the specified value.
     */
    public static int hash(float value) {
        assert !Float.isNaN(value) : "Values of NaN are not supported.";

        return Float.floatToIntBits(value*663608941.737f);
        // this avoids excessive hashCollisions in the case values are
        // of the form (1.0, 2.0, 3.0, ...)
    }

    /**
     * Returns a hashcode for the specified value.
     *
     * @return  a hash code value for the specified value.
     */
    public static int hash(int value) {
		return value;
    }

    /**
     * Returns a hashcode for the specified value.
     *
     * @return  a hash code value for the specified value.
     */
    public static int hash(long value) {
        return ((int)(value ^ (value >>> 32)));
    }

    /**
     * Returns a hashcode for the specified object.
     *
     * @return  a hash code value for the specified object.
     */
    public static int hash(Object object) {
        return object==null ? 0 : object.hashCode();
    }


    /**
     * In profiling, it has been found to be faster to have our own local implementation
     * of "ceil" rather than to call to {@link Math#ceil(double)}.
     */
    public static int fastCeil( float v ) {
        int possible_result = ( int ) v;
        if ( v - possible_result > 0 ) possible_result++;
        return possible_result;
    }
}