org.h2.dev.hash

Class MinimalPerfectHash.StringHash

java.lang.Object

org.h2.dev.hash.MinimalPerfectHash.StringHash

All Implemented Interfaces:

MinimalPerfectHash.UniversalHash<java.lang.String>

Enclosing class:

MinimalPerfectHash<K>

public static class MinimalPerfectHash.StringHash
extends java.lang.Object
implements MinimalPerfectHash.UniversalHash<java.lang.String>

A sample hash implementation for integer keys.

Constructor Summary

Constructors

Constructor and Description
StringHash()

Method Summary

Modifier and Type	Method and Description
static int	getFastHash(java.lang.String o, int index, int seed) A cryptographically weak hash function.
static int	getSipHash24(byte[] b, int start, int end, long k0, long k1) A cryptographically relatively secure hash function.
static int	getSipHash24(java.lang.String o, long k0, long k1) A cryptographically relatively secure hash function.
int	hashCode(java.lang.String o, int index, int seed) Calculate the hash of the given object.

Methods inherited from class java.lang.Object

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

Constructor Detail

StringHash

public StringHash()

Method Detail

hashCode

public int hashCode(java.lang.String o,
                    int index,
                    int seed)

Description copied from interface: MinimalPerfectHash.UniversalHash

Calculate the hash of the given object.

Specified by:

hashCode in interface MinimalPerfectHash.UniversalHash<java.lang.String>

Parameters:

o - the object

index - the hash function index (index 0 is used first, so the method should be very fast with index 0; index 1 and so on are only called when really needed)

seed - the random seed (always the same for a hash table)

Returns:

the hash value

getFastHash

public static int getFastHash(java.lang.String o,
                              int index,
                              int seed)

A cryptographically weak hash function. It is supposed to be fast.

Parameters:

o - the string

index - the hash function index

seed - the seed

Returns:

the hash value

getSipHash24

public static int getSipHash24(java.lang.String o,
                               long k0,
                               long k1)

A cryptographically relatively secure hash function. It is supposed to protected against hash-flooding denial-of-service attacks.

Parameters:

o - the string

k0 - key 0

k1 - key 1

Returns:

the hash value

getSipHash24

public static int getSipHash24(byte[] b,
                               int start,
                               int end,
                               long k0,
                               long k1)

A cryptographically relatively secure hash function. It is supposed to protected against hash-flooding denial-of-service attacks.

Parameters:

b - the data

start - the start position

end - the end position plus one

k0 - key 0

k1 - key 1

Returns:

the hash value