@ably/bloomit

A fork of the bloomit package to fix a few issues (eg https://github.com/kblauhut/bloomit/issues/4 ) and switch from xxhash to farmhash.

Original readme follows below.

bloomit

bloomit is a Space efficient bloom filter based on the bloom-filters npm package.

The main motivation for this package was to reduce the memory usage of the bloom filter by using a bitmap instead of an array of javascript numbers. This should result in a theoretical memory reduction by a factor of 64.

I have also edited the export to use a Uint8Array which encodes all needed values and can be used to send it over the web efficiently.

Methods

• add(element: string) -> void: add an element into the filter.
• has(element: string) -> boolean: Test an element for membership, returning False if the element is definitively not in the filter and True is the element might be in the filter.
• equals(other: BloomFilter) -> boolean: Test if two filters are equals.
• rate() -> number: compute the filter's false positive rate (or error rate).
• export() -> Uint8Array: export the filter as an Uint8Array
• inport(filterUint8Array: Uint8Array) -> BloomFilter: Create a filter from a exporterd Uint8Array

1const { BloomFilter } = require('bloomit');
2// create a Bloom Filter with a size of 10 and 4 hash functions
3let filter = new BloomFilter(10, 4);
4// insert data
5filter.add('paul');
6filter.add('kolja');
7filter.add('carl');
8
9// lookup for some data
10console.log(filter.has('paul')); // output: true
11console.log(filter.has('xiaomei')); // output: false
12
13// print the error rate
14console.log(filter.rate());
15
16// alternatively, create a bloom filter optimal for a number of items and a desired error rate
17const items = ['paul', 'kolja', 'carl'];
18const errorRate = 0.04; // 4 % error rate
19filter = BloomFilter.create(items.length, errorRate);
20
21// or create a bloom filter optimal for a collections of items and a desired error rate
22filter = BloomFilter.from(items, errorRate);
23
24// Export the filter
25const exportedFilter = filter.export();
26
27// Import the filter
28filter = BloomFilter.import(exportedFilter);