// 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; /** * Provides various hash functions. * * @author wolfgang.hoschek@cern.ch * @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 final 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 final 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 *
* using* 31^5*(d[0]*31^(n-1) + d[1]*31^(n-2) + ... + d[n-1]) *
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 final 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 final int hash(long value) {
return (int)(value ^ (value >> 32));
/*
* The hashcode is computed as
* * using* 31^5*(d[0]*31^(n-1) + d[1]*31^(n-2) + ... + d[n-1]) *
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 final int hash(Object object) {
return object==null ? 0 : object.hashCode();
}
}