org.apache.sysds.utils

Class Hash

java.lang.Object

org.apache.sysds.utils.Hash

public class Hash
extends Object

A class containing different hashing functions.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Hash.HashType Available Hashing techniques

Constructor Summary

Constructors

Constructor and Description
Hash()

Method Summary

Modifier and Type	Method and Description
static byte	expHash(int x) Compute exponentially distributed hash values in range 0..a.length eg: 50% == 0 , 25% == 1 12.5 % == 2 etc.
static int	hash(double o, Hash.HashType ht) Hash functions for double values.
static int	hash(Object o, Hash.HashType ht) Generic hashing of java objects, not ideal for specific values so use the specific methods for specific types.
static int	linearHash(int v) Compute the Linear hash of an int input value.
static int	linearHash(int v, int bits) Compute the Linear hash of an int input value, but only use the first bits of the linear hash.

Methods inherited from class java.lang.Object

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

Constructor Detail

Hash

public Hash()

Method Detail

hash

public static int hash(Object o,
                       Hash.HashType ht)

Generic hashing of java objects, not ideal for specific values so use the specific methods for specific types. To Use the locality sensitive techniques override the objects hashcode function.

Parameters:

o - The Object to hash.

ht - The HashType to use.

Returns:

An int Hash value.

hash

public static int hash(double o,
                       Hash.HashType ht)

Hash functions for double values.

Parameters:

o - The double value.

ht - The hashing function to apply.

Returns:

An int Hash value.

linearHash

public static int linearHash(int v)

Compute the Linear hash of an int input value.

Parameters:

v - The value to hash.

Returns:

The int hash.

linearHash

public static int linearHash(int v,
                             int bits)

Compute the Linear hash of an int input value, but only use the first bits of the linear hash.

Parameters:

v - The value to hash.

bits - The number of bits to use. up to maximum of 32.

Returns:

The hashed value

expHash

public static byte expHash(int x)

Compute exponentially distributed hash values in range 0..a.length eg: 50% == 0 , 25% == 1 12.5 % == 2 etc. Useful because you can estimate size of a collection by only maintaining the highest value found. from this hash.

Parameters:

x - value to hash

Returns:

a hash value byte (only in the range of 0 to a.length)