avail/avail.utility.structures/BloomFilter

BloomFilter

A BloomFilter is a conservative, probabilistic set. It can report that an element is probably in the set, or definitely not in the set. This can be a useful, fast prefilter to avoid computing or fetching authoritative data in a large majority of cases, effectively reducing the number of spurious occurrences of the slower activity by orders of magnitude.

Since the filter is probabilistic, the interface is defined entirely in terms of Ints, under the assumption that the actual entity being tested for membership has already been hashed.

Author

Mark van Gulik

Parameters

The type of objects hashed into the filter.

Constructors

BloomFilter

constructor(bitCount: Int, hashCount: Int)

Construct a new instance that initially reports false for every membership test. If a non-null existingFilter is provided, it is copied instead.

constructor(existingFilter: BloomFilter<T>)

Copy an existing BloomFilter.

constructor(binaryStream: DataInputStream)

Reconstruct a BloomFilter previously written by write.

Types

Companion

object Companion

Properties

bitCount

val bitCount: Int

The number of bit positions in the filter.

Functions

add

fun add(element: T)

Add an element (T) to the filter.

addAll

fun addAll(filter: BloomFilter<T>)

Add all elements of the given BloomFilter to the receiver. The array size and hashCount of the given filter should match that of the receiver.

addHash

fun addHash(elementHash: Int)

Add an Int, the hashCode of some element, to the BloomFilter.

get

operator fun get(element: T): Boolean

Determine whether the given element is probably present in the filter. If the element is present, this always returns true, but it may sometimes return true even if the element is not present.

getByHash

fun getByHash(elementHash: Int): Boolean

Determine whether an element with the given hashCode is probably present in the filter. If the element is present, this always returns true, but it may sometimes return true even if the element is not present.

write

fun write(binaryStream: DataOutputStream)

Write this BloomFilter onto the given stream, such that the constructor taking a DataInputStream can reconstruct it.