gnu.trove.HashFunctions Maven / Gradle / Ivy
// 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 [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) {
// Multiply by prime to make sure hash can't be negative (see Knuth v3, p. 515-516)
return value * 31;
}
/**
* Returns a hashcode for the specified value.
*
* @return a hash code value for the specified value.
*/
public static int hash(long value) {
// Multiply by prime to make sure hash can't be negative (see Knuth v3, p. 515-516)
return ((int)(value ^ (value >>> 32))) * 31;
}
/**
* 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)}.
*/
static int fastCeil( float v ) {
int possible_result = ( int ) v;
if ( v - possible_result > 0 ) possible_result++;
return possible_result;
}
}