C# Class StopGuessing.DataStructures.FilterArray

A FilterArray is a bit array that contains additional methods to support probabilistic data structures that map elements (keys) to a set of deterministic, pseudorandom indexes in the bit array. These methods support data structures such as bloom filters and binomial ladder filters that store information about an element within the bits at the indexes that are pseudorandomly associated with the element.

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Protected Properties

Property	Type	Description
BitArray	System.Collections.BitArray
HashFunctionsMappingElementsToBitsInTheArray	StopGuessing.EncryptionPrimitives.UniversalHashFunction[]

Public Methods

Method	Description
AssignBit ( int indexOfTheBitToAssign, bool desiredValue ) : bool	Assign the bit at a given index to a desired value, and return true if and only if the bit was already set to that value.
AssignRandomBit ( int value ) : void	Assign the value of either zero or one to a randomly-selected bit of the filter array.
ClearBitToZero ( int indexOfBitToClear ) : bool	Clear the bit an in index to zero (false).
ClearRandomBitToZero ( ) : void	Clear a randomly-selected bit of the filter array to zero.
FilterArray ( int numberOfBitsInArray, int maximumBitIndexesPerElement, bool initilizeBitsOfArrayAtRandom, string saltForHashFunctions = "" ) : System	Construct a filter array.
GetIndexesAssociatedWithAnElement ( byte element, int numberOfIndexesRequested = null ) : IEnumerable	Map a element to its corresponding bits in the array.
GetIndexesAssociatedWithAnElement ( string element, int numberOfIndexesRequested = null ) : IEnumerable	Get the set of indexes associated with an element.
SetBitToOne ( int indexOfBitToSet ) : bool	Set the bit an in index to one (true).
SetRandomBitToOne ( ) : void	Set a randomly-selected bit of the filter array to one.
SwapBits ( int indexA, int indexB ) : void	Swap the values of the bits at two indexes into the filter array.
this ( int index ) : bool	Read or write bits of the filter array directly.

Method Details

AssignBit() public method

Assign the bit at a given index to a desired value, and return true if and only if the bit was already set to that value.

public AssignBit ( int indexOfTheBitToAssign, bool desiredValue ) : bool
indexOfTheBitToAssign	int	The index of the bit to set.
desiredValue	bool	The value to set the bit to.
return	bool

AssignRandomBit() public method

Assign the value of either zero or one to a randomly-selected bit of the filter array.

public AssignRandomBit ( int value ) : void
value	int	The value to be assigned. Passing 0 causes a value 0 (false) to be stored /// and passing any other value causes a one (true) to be stored in the randomly-selected bit.
return	void

ClearBitToZero() public method

Clear the bit an in index to zero (false).

public ClearBitToZero ( int indexOfBitToClear ) : bool
indexOfBitToClear	int	The index of the bit to clear.
return	bool

ClearRandomBitToZero() public method

Clear a randomly-selected bit of the filter array to zero.

public ClearRandomBitToZero ( ) : void
return	void

FilterArray() public method

Construct a filter array.

public FilterArray ( int numberOfBitsInArray, int maximumBitIndexesPerElement, bool initilizeBitsOfArrayAtRandom, string saltForHashFunctions = "" ) : System
numberOfBitsInArray	int	The size of the array in bits.
maximumBitIndexesPerElement	int	The maximum (and default) number of indexes (bits) in the array to associate with elements.
initilizeBitsOfArrayAtRandom	bool	If set to true, the bits of the filter array will be set to 0 or 1 at random (indpendently, each with probability 0.5).
saltForHashFunctions	string	A salt used to generate the hash functions. /// Any two filter arrays generated with the same salt will use the same hash functions. /// The salt should be kept secret from attackerse who might try to manipulate the selection of elements, /// such as to intentionally cause bit collisions with the array.
return	System

GetIndexesAssociatedWithAnElement() public method

Map a element to its corresponding bits in the array.

public GetIndexesAssociatedWithAnElement ( byte element, int numberOfIndexesRequested = null ) : IEnumerable
element	byte	The element to be mapped to indexes
numberOfIndexesRequested	int	The number of indexes to associate with the element. If not set, /// uses the MaximumBitIndexesPerElement specified in the constructor.
return	IEnumerable

GetIndexesAssociatedWithAnElement() public method

Get the set of indexes associated with an element.

public GetIndexesAssociatedWithAnElement ( string element, int numberOfIndexesRequested = null ) : IEnumerable
element	string	The value that should be associated with a set of indexes.
numberOfIndexesRequested	int	The optional number of indexes to associate with the element. If not provided, /// the number of indexes returned will be equal to the default (MaximumBitIndexesPerElement) set in the constructor.
return	IEnumerable

SetBitToOne() public method

Set the bit an in index to one (true).

public SetBitToOne ( int indexOfBitToSet ) : bool
indexOfBitToSet	int	The index of the bit to set.
return	bool

SetRandomBitToOne() public method

Set a randomly-selected bit of the filter array to one.

public SetRandomBitToOne ( ) : void
return	void

SwapBits() public method

Swap the values of the bits at two indexes into the filter array.

public SwapBits ( int indexA, int indexB ) : void
indexA	int	Index to the first of the two bits to swap.
indexB	int	Index to the second of the two bits to swap.
return	void

this() public method

Read or write bits of the filter array directly.

public this ( int index ) : bool
index	int	The index of the bit to read/write.
return	bool

Property Details

BitArray protected property

The bit array used by a filter

protected BitArray,System.Collections BitArray
return	System.Collections.BitArray

HashFunctionsMappingElementsToBitsInTheArray protected property

The hash functions used to index into the bit array to map elements to a set of bits

protected UniversalHashFunction[],StopGuessing.EncryptionPrimitives HashFunctionsMappingElementsToBitsInTheArray
return	StopGuessing.EncryptionPrimitives.UniversalHashFunction[]