bloom-filter

About

Bloom filters can very quickly answer variations on the Yes/No question “is this item in the set?”, like “have I seen this item before?”

• WIKI
• Bloom filters by example
• fun read about bloom filters and their value
• white paper
• c++ example

While bloom filters can give false positives, they cannot give false negatives. When

Install

// NPM
npm install --save @polkajs/bloom-filter
// YARN
yarn add @polkajs/bloom-filter

Use

const Bloom = require('@polkajs/bloom-filter').default;

let bloom = new Bloom(16, 8); // 16 byte length, assuming max 8 inputs
B.add("cat");
B.add("parrot");
B.add("monkey");

console.log(B);
// Bloom {
//   bitmapBits: 128,
//   k: 2,
//   bitmap: <Buffer 00 00 80 00 00 00 08 00 00 20 01 00 88 00 00 00>,
//   numHashes: 8,
//   hashFunc: [Function]
// }

let dog = B.inSet("dog");
let cat = B.inSet("cat");

console.log("is 'dog' in the set?", dog);
// false
console.log("is 'cat' in the set?", cat);
// true
console.log(B.toString());
// 00008000000008000020010088000000

API

new

create a new bloom

new Bloom(size: number, numHashes: number, hashFunc?: Function)

• size: number of bytes in bloom map
• numHashes: max number of inputs
• hashFun: [OPTIONAL] replace the murmurhash3 algorithm

add

add a new input

bloom.add(data: string)

• data: input string to be mapped

inSet

check if a value exists in the bloom filter set

bloom.inset(data: string): bool

• data: input string to be checked

toString

hexadecimal string of the current mapping of inputs

bloom.toString(): string

extendBloom

takes

bloom.extendBloom(b: Bloom): Bloom

• b bloom filter to extend from

ISC License (ISC)

Copyright 2017 Copyright (c) 2004-2010 by Internet Systems Consortium, Inc. ("ISC") Copyright (c) 1995-2003 by Internet Software Consortium

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.