com.squareup.haha.trove.HashFunctions Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of haha Show documentation
Java library to automate the analysis of Android heap dumps.
There is a newer version: 2.1
// 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 com.squareup.haha.trove;

/**
 * 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) {
        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) {
        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. The hashcode is computed as
     *  
     * 31^5*(d[0]*31^(n-1) + d[1]*31^(n-2) + ... + d[n-1])
     * 
     * using int arithmetic, where d[i] is
     * the ith digit of the value, counting from the right,
     * n is the number of decimal digits of the specified
     * value, and ^ indicates exponentiation.  (The hash
     * value of the value zero is zero.)
     *
     * @return  a hash code value for the specified value. 
     */
    public static int hash(int value) {
        //return value * 0x278DDE6D; // see cern.jet.random.engine.DRand
	
        return value;
	
        /*
          value &= 0x7FFFFFFF; // make it >=0
          int hashCode = 0;
          do hashCode = 31*hashCode + value%10;
          while ((value /= 10) > 0);

          return 28629151*hashCode; // spread even further; h*31^5
        */
    }

    /**
     * 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));

        /*
         * The hashcode is computed as
         *  
         * 31^5*(d[0]*31^(n-1) + d[1]*31^(n-2) + ... + d[n-1])
         * 
         * using int arithmetic, where d[i] is the 
         * ith digit of the value, counting from the right, n is the number of decimal digits of the specified value,
         * and ^ indicates exponentiation.
         * (The hash value of the value zero is zero.)
 
         value &= 0x7FFFFFFFFFFFFFFFL; // make it >=0 (0x7FFFFFFFFFFFFFFFL==Long.MAX_VALUE)
         int hashCode = 0;
         do hashCode = 31*hashCode + (int) (value%10);
         while ((value /= 10) > 0);

         return 28629151*hashCode; // spread even further; h*31^5
        */
    }

    /**
     * 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();
    }
}