Package org.wildfly.common.math

Class HashMath

java.lang.Object

org.wildfly.common.math.HashMath

public final class HashMath
extends java.lang.Object

Routines which are useful for hashcode computation, among other things.

Author:

David M. Lloyd

Method Summary

Modifier and Type	Method	Description
static int	multiHashOrdered(int accumulatedHash, int nextHash)	A hash function which combines an accumulated hash with a next hash such that f(f(k, b), a) \u2260\u2099 f(f(k, a), b).
static int	multiHashOrdered(int accumulatedHash, int prime, int nextHash)	A hash function which combines an accumulated hash with a next hash such that f(f(k, p2, b), p1, a) \u2260\u2099 f(f(k, p1, a), p2, b).
static int	multiHashUnordered(int accumulatedHash, int nextHash)	A hash function which combines an accumulated hash with a next hash such that f(f(k, b), a) = f(f(k, a), b).
static int	multiHashUnordered(int accumulatedHash, int prime, int nextHash)	A hash function which combines an accumulated hash with a next hash such that f(f(k, p2, b), p1, a) = f(f(k, p1, a), p2, b).
static int	multiplyWrap(int a, int b)	Multiply two unsigned integers together.
static int	roundToPowerOfTwo(int value)	Round the given value up to the next positive power of two.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

roundToPowerOfTwo

public static int roundToPowerOfTwo(int value)

Round the given value up to the next positive power of two.

Parameters:

value - the value (must not be negative and must be less than or equal to 2^31)

Returns:

the rounded power of two value

multiHashOrdered

public static int multiHashOrdered(int accumulatedHash,
                                   int prime,
                                   int nextHash)

A hash function which combines an accumulated hash with a next hash such that f(f(k, p2, b), p1, a) \u2260\u2099 f(f(k, p1, a), p2, b). This function is suitable for object chains whose order affects the overall equality of the hash code.

The exact algorithm is not specified and is therefore subject to change and should not be relied upon for hash codes that persist outside of the JVM process.

Parameters:

accumulatedHash - the accumulated hash code of the previous stage

prime - a prime multiplier

nextHash - the hash code of the next single item

Returns:

the new accumulated hash code

multiHashUnordered

public static int multiHashUnordered(int accumulatedHash,
                                     int prime,
                                     int nextHash)

A hash function which combines an accumulated hash with a next hash such that f(f(k, p2, b), p1, a) = f(f(k, p1, a), p2, b). This function is suitable for object chains whose order does not affect the overall equality of the hash code.

The exact algorithm is not specified and is therefore subject to change and should not be relied upon for hash codes that persist outside of the JVM process.

Parameters:

accumulatedHash - the accumulated hash code of the previous stage

prime - a prime multiplier

nextHash - the hash code of the next single item

Returns:

the new accumulated hash code

multiHashOrdered

public static int multiHashOrdered(int accumulatedHash,
                                   int nextHash)

A hash function which combines an accumulated hash with a next hash such that f(f(k, b), a) \u2260\u2099 f(f(k, a), b). This function is suitable for object chains whose order affects the overall equality of the hash code.

The exact algorithm is not specified and is therefore subject to change and should not be relied upon for hash codes that persist outside of the JVM process.

Parameters:

accumulatedHash - the accumulated hash code of the previous stage

nextHash - the hash code of the next single item

Returns:

the new accumulated hash code

multiHashUnordered

public static int multiHashUnordered(int accumulatedHash,
                                     int nextHash)

A hash function which combines an accumulated hash with a next hash such that f(f(k, b), a) = f(f(k, a), b). This function is suitable for object chains whose order does not affect the overall equality of the hash code.

The exact algorithm is not specified and is therefore subject to change and should not be relied upon for hash codes that persist outside of the JVM process.

Parameters:

accumulatedHash - the accumulated hash code of the previous stage

nextHash - the hash code of the next single item

Returns:

the new accumulated hash code

multiplyWrap

public static int multiplyWrap(int a,
                               int b)

Multiply two unsigned integers together. If the result overflows a 32-bit number, XOR the overflowed bits back into the result. This operation is commutative, i.e. if we designate the \u2a30 symbol to represent this operation, then a \u2a30 b = b \u2a30 a. This operation is not associative, i.e. (a \u2a30 b) \u2a30 c \u2260\u2099 a \u2a30 (b \u2a30 c) (the symbol \u2260\u2099 meaning "not necessarily equal to"), therefore this operation is suitable for ordered combinatorial hash functions.

Parameters:

a - the first number to multiply

b - the second number to multiply

Returns:

the wrapped multiply result