jdd.util.math

Class HashFunctions

java.lang.Object

jdd.util.math.HashFunctions

public final class HashFunctions
extends Object

This class contains some useful (?) hash functions.

Note: the hash numbers may be smaller than zero. you may AND them with the mask 0x7FFFFFFF to fix that.

Each hash function in good in its own place. for example, pair() may give bad results in the chi^2 test, but it is the better hash in some situations.

Constructor Summary

Constructors

Constructor and Description
HashFunctions()

Method Summary

Modifier and Type	Method and Description
static int	hash_FNV(int[] data, int offset, int len) hash the 32-bit array with FNV
static int	hash_FNV(int a, int b, int c) 32-bit hash of FNV with 3 32-bit words input.
static int	hash_jenkins(int a, int b, int c) This hash function was suggested by Bob Jenkins (of Oracle).
static int	hash_pair(int a, int b) pair-hash for two elements
static int	hash_pair(int a, int b, int c) pair-hash for three elements
static int	hash_prime(int a, int b) prime-hash for two elements
static int	hash_prime(int a, int b, int c) prime-hash for three elements
static void	internal_test()
static int	mix_jenkins(int i) Robert Jenkins' bit mix function
static int	mix_wang(int i) Thomas Wang's 32 bit mix function
static int	mix(int i) mix the bits in i in some clever way.

Methods inherited from class java.lang.Object

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

Constructor Detail

HashFunctions

public HashFunctions()

Method Detail

mix

public static final int mix(int i)

mix the bits in i in some clever way.

Use this one when you dont know much about i. NOTE: it is slower then the others

mix_wang

public static final int mix_wang(int i)

Thomas Wang's 32 bit mix function

mix_jenkins

public static final int mix_jenkins(int i)

Robert Jenkins' bit mix function

hash_pair

public static final int hash_pair(int a,
                                  int b)

pair-hash for two elements

hash_pair

public static final int hash_pair(int a,
                                  int b,
                                  int c)

pair-hash for three elements

hash_prime

public static final int hash_prime(int a,
                                   int b)

prime-hash for two elements

hash_prime

public static final int hash_prime(int a,
                                   int b,
                                   int c)

prime-hash for three elements

hash_jenkins

public static final int hash_jenkins(int a,
                                     int b,
                                     int c)

This hash function was suggested by Bob Jenkins (of Oracle). It performs equally well, but is a bit slower than the others.

hash_FNV

public static final int hash_FNV(int a,
                                 int b,
                                 int c)

32-bit hash of FNV with 3 32-bit words input.

This hash functions is probably best for strings than 3-tupple integers.

hash_FNV

public static final int hash_FNV(int[] data,
                                 int offset,
                                 int len)

hash the 32-bit array with FNV

internal_test

public static void internal_test()