C# Class Demo.Library.Algorithms.Bloom.CuckooBloomFilter

CuckooFilter implements a Cuckoo Bloom filter as described by Andersen, Kaminsky, and Mitzenmacher in Cuckoo Filter: Practically Better Than Bloom: http://www.pdl.cmu.edu/PDL-FTP/FS/cuckoo-conext2014.pdf A Cuckoo Filter is a Bloom filter variation which provides support for removing elements without significantly degrading space and performance. It works by using a cuckoo hashing scheme for inserting items. Instead of storing the elements themselves, it stores their fingerprints which also allows for item removal without false negatives (if you don't attempt to remove an item not contained in the filter). For applications that store many items and target moderately low false-positive rates, cuckoo filters have lower space overhead than space-optimized Bloom filters.

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Private Properties

Property	Type	Description
CalculateF	uint
ComputeHash	byte[]
ComputeHashSum32	uint
Contains	bool
GetComponents	Components
GetEmptyEntry	int
IndexOf	int
Insert	bool
Power2	uint

Public Methods

Method	Description
Add ( byte data ) : bool	Will add the data to the Cuckoo Filter. It returns false if the filter is full. If the filter is full, an item is removed to make room for the new item. This introduces a possibility for false negatives. To avoid this, use Count and Capacity to check if the filter is full before adding an item.
BucketCount ( ) : uint	Returns the number of buckets.
Capacity ( ) : uint	Returns the number of items the filter can store.
Count ( ) : uint	Returns the number of items in the filter.
CuckooBloomFilter ( uint n, double fpRate ) : System	Creates a new Cuckoo Bloom filter optimized to store n items with a specified target false-positive rate.
Reset ( ) : CuckooBloomFilter	Restores the Bloom filter to its original state. It returns the filter to allow for chaining.
SetHash ( HashAlgorithm h ) : void	Sets the hashing function used in the filter.
Test ( byte data ) : bool	Will test for membership of the data and returns true if it is a member, false if not. This is a probabilistic test, meaning there is a non-zero probability of false positives.
TestAndAdd ( byte data ) : TestAndAddReturnValue	Equivalent to calling Test followed by Add. It returns (true, false) if the data is a member, (false, add()) if not. False is returned if the filter is full. If the filter is full, an item is removed to make room for the new item. This introduces a possibility for false negatives. To avoid this, use Count and Capacity to check if the filter is full before adding an item.
TestAndRemove ( byte data ) : bool	Will test for membership of the data and remove it from the filter if it exists. Returns true if the data was a member, false if not.

Private Methods

Method	Description
CalculateF ( uint b, double epsilon ) : uint	Returns the optimal fingerprint length in bytes for the given bucket size and false-positive rate epsilon.
ComputeHash ( byte data ) : byte[]	Returns a 32-bit hash value for the given data.
ComputeHashSum32 ( byte data ) : uint	Returns the sum of the hash.
Contains ( byte bucket, byte f ) : bool	Indicates if the given fingerprint is contained in one of the bucket's entries.
GetComponents ( byte data ) : Components	Returns the two hash values used to index into the buckets and the fingerprint for the given element.
GetEmptyEntry ( byte bucket ) : int	Returns the index of the next available entry in the bucket or -1 if it's full.
IndexOf ( byte bucket, byte f ) : int	Returns the entry index of the given fingerprint or -1 if it's not in the bucket.
Insert ( uint i1, uint i2, byte f ) : bool	Will insert the fingerprint into the filter returning false if the filter is full.
Power2 ( uint x ) : uint	Calculates the next power of two for the given value.

Method Details

Add() public method

Will add the data to the Cuckoo Filter. It returns false if the filter is full. If the filter is full, an item is removed to make room for the new item. This introduces a possibility for false negatives. To avoid this, use Count and Capacity to check if the filter is full before adding an item.

public Add ( byte data ) : bool
data	byte
return	bool

BucketCount() public method

Returns the number of buckets.

public BucketCount ( ) : uint
return	uint

Capacity() public method

Returns the number of items the filter can store.

public Capacity ( ) : uint
return	uint

Count() public method

Returns the number of items in the filter.

public Count ( ) : uint
return	uint

CuckooBloomFilter() public method

Creates a new Cuckoo Bloom filter optimized to store n items with a specified target false-positive rate.

public CuckooBloomFilter ( uint n, double fpRate ) : System
n	uint	Number of items to store
fpRate	double	Target false-positive rate
return	System

Reset() public method

Restores the Bloom filter to its original state. It returns the filter to allow for chaining.

public Reset ( ) : CuckooBloomFilter
return	CuckooBloomFilter

SetHash() public method

Sets the hashing function used in the filter.

public SetHash ( HashAlgorithm h ) : void
h	System.Security.Cryptography.HashAlgorithm	The HashAlgorithm to use.
return	void

Test() public method

Will test for membership of the data and returns true if it is a member, false if not. This is a probabilistic test, meaning there is a non-zero probability of false positives.

public Test ( byte data ) : bool
data	byte	The data to test for
return	bool

TestAndAdd() public method

Equivalent to calling Test followed by Add. It returns (true, false) if the data is a member, (false, add()) if not. False is returned if the filter is full. If the filter is full, an item is removed to make room for the new item. This introduces a possibility for false negatives. To avoid this, use Count and Capacity to check if the filter is full before adding an item.

public TestAndAdd ( byte data ) : TestAndAddReturnValue
data	byte
return	TestAndAddReturnValue

TestAndRemove() public method

Will test for membership of the data and remove it from the filter if it exists. Returns true if the data was a member, false if not.

public TestAndRemove ( byte data ) : bool
data	byte	Data to test for and remove
return	bool