orestes.bloomfilter

Enum HashProvider.HashMethod

java.lang.Object

java.lang.Enum<HashProvider.HashMethod>

orestes.bloomfilter.HashProvider.HashMethod

All Implemented Interfaces:

java.io.Serializable, java.lang.Comparable<HashProvider.HashMethod>

Enclosing class:

HashProvider

public static enum HashProvider.HashMethod
extends java.lang.Enum<HashProvider.HashMethod>

Different types of hash functions that can be used.

Enum Constant Summary

Enum Constants

Enum Constant and Description
Adler32 Generates hash values using the Adler32 Checksum algorithm.
CarterWegman Generates hash values using the Carter Wegman function (Wikipedia), which is a universal hashing function.
CRC32 Generates hash values using a Cyclic Redundancy Check (CRC32).
FNVWithLCG Uses the Fowler–Noll–Vo (FNV) hash function to generate a hash values.
MD2 Generates a hash value using MD2.
MD5 Generates a hash value using the cryptographic MD5 hash function.
Murmur2 Generates hash values using the Murmur 2 hash, see: https://code.google.com/p/smhasher/wiki/MurmurHash2 Murmur 2 is very fast.
Murmur3 Generates hash values using the Murmur 3 hash, see: https://code.google.com/p/smhasher/wiki/MurmurHash3 Its uniformity is comparable to that of cryptographic hash functions but considerably faster.
Murmur3KirschMitzenmacher Uses a the Murmur 3 hash in combination with a performance optimization described by Kirsch and Mitzenmacher, see: http://www.eecs.harvard.edu/~kirsch/pubs/bbbf/esa06.pdf - hash values are generated through the scheme h_i = (h1 + i*h2) mod m Though this method is asymptotically optimal our experiements revealed that real-world performance is not as good as pure Murmur 3 hashes or cryptographic hash functions, in particular for random words.
RNG Generates hash values using the Java Random Number Generator (RNG) which is a Linear Congruential Generator (LCG), implementing the following formula: number_i+1 = (a * number_i + countingBits) mod size The RNG is initialized using the value to be hashed.
SHA1 Generates a hash value using the cryptographic SHA1 hash function.
SHA256 Generates a hash value using the cryptographic SHA-256 hash function.
SHA384 Generates a hash value using the cryptographic SHA-384 hash function.
SHA512 Generates a hash value using the cryptographic SHA-512 hash function.

Method Summary

Modifier and Type	Method and Description
HashProvider.HashFunction	getHashFunction()
static HashProvider.HashMethod	valueOf(java.lang.String name) Returns the enum constant of this type with the specified name.
static HashProvider.HashMethod[]	values() Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

RNG

public static final HashProvider.HashMethod RNG

Generates hash values using the Java Random Number Generator (RNG) which is a Linear Congruential Generator (LCG), implementing the following formula:
number_i+1 = (a * number_i + countingBits) mod size

The RNG is initialized using the value to be hashed.

CarterWegman

public static final HashProvider.HashMethod CarterWegman

Generates hash values using the Carter Wegman function (Wikipedia), which is a universal hashing function. It thus has optimal guarantees for the uniformity of generated hash values. On the downside, the performance is not optimal, as arithmetic operations on large numbers have to be performed.

CRC32

public static final HashProvider.HashMethod CRC32

Generates hash values using a Cyclic Redundancy Check (CRC32). CRC is designed as a checksum for data integrity not as hash function but exhibits very good uniformity and is relatively fast.

Adler32

public static final HashProvider.HashMethod Adler32

Generates hash values using the Adler32 Checksum algorithm. Adler32 is comparable to CRC32 but is faster at the cost of a less uniform distribution of hash values.

Murmur2

public static final HashProvider.HashMethod Murmur2

Generates hash values using the Murmur 2 hash, see: https://code.google.com/p/smhasher/wiki/MurmurHash2

Murmur 2 is very fast. However, there is a flaw that affects the uniformity of some input values (for instance increasing integers as strings).

Murmur3

public static final HashProvider.HashMethod Murmur3

Generates hash values using the Murmur 3 hash, see: https://code.google.com/p/smhasher/wiki/MurmurHash3

Its uniformity is comparable to that of cryptographic hash functions but considerably faster.

Murmur3KirschMitzenmacher

public static final HashProvider.HashMethod Murmur3KirschMitzenmacher

Uses a the Murmur 3 hash in combination with a performance optimization described by Kirsch and Mitzenmacher, see: http://www.eecs.harvard.edu/~kirsch/pubs/bbbf/esa06.pdf - hash values are generated through the scheme h_i = (h1 + i*h2) mod m

Though this method is asymptotically optimal our experiements revealed that real-world performance is not as good as pure Murmur 3 hashes or cryptographic hash functions, in particular for random words.

FNVWithLCG

public static final HashProvider.HashMethod FNVWithLCG

Uses the Fowler–Noll–Vo (FNV) hash function to generate a hash values. It is superior to the standard implementation in Arrays and can be easily implemented in most languages. Hashing then uses the very simple Linear Congruential Generator scheme and the Java initialization constants. This method is intended to be employed if the bloom filter has to be used in a language which doesn't support any of the other hash functions. This hash function can then easily be implemented.

MD2

public static final HashProvider.HashMethod MD2

Generates a hash value using MD2. MD2 is rather slow an not as evenely distributed as other cryptographic hash functions

MD5

public static final HashProvider.HashMethod MD5

Generates a hash value using the cryptographic MD5 hash function. It is fast and has good guarantees for the uniformity of generated hash values, as the hash functions are designed for cryptographic use.

SHA1

public static final HashProvider.HashMethod SHA1

Generates a hash value using the cryptographic SHA1 hash function. It is fast but uniformity of hash values is better for the second generation of SHA (256,384,512).

SHA256

public static final HashProvider.HashMethod SHA256

Generates a hash value using the cryptographic SHA-256 hash function. It is fast and has good guarantees for the uniformity of generated hash values, as the hash functions are designed for cryptographic use.

SHA384

public static final HashProvider.HashMethod SHA384

Generates a hash value using the cryptographic SHA-384 hash function. It is fast and has good guarantees for the uniformity of generated hash values, as the hash functions are designed for cryptographic use.

SHA512

public static final HashProvider.HashMethod SHA512

Generates a hash value using the cryptographic SHA-512 hash function. It is fast and has good guarantees for the uniformity of generated hash values, as the hash functions are designed for cryptographic use.

Method Detail

values

public static HashProvider.HashMethod[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (HashProvider.HashMethod c : HashProvider.HashMethod.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static HashProvider.HashMethod valueOf(java.lang.String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

java.lang.IllegalArgumentException - if this enum type has no constant with the specified name

java.lang.NullPointerException - if the argument is null

getHashFunction

public HashProvider.HashFunction getHashFunction()