BitSet.js


BitSet.js is an infinite Bit-Array (aka bit vector, bit string, bit set) implementation in JavaScript. Infinite means that if you invert a bit vector, the leading ones get remembered. As far as I can tell, BitSet.js is the only library which has this feature. It is also heavily benchmarked against other implementations and is the most performant implementation to date.

Examples

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``javascript
let bs = new BitSet;
bs.set(128, 1); // Set bit at position 128
console.log(bs.toString(16)); // Print out a hex dump with one bit set
`

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`javascript
let bs = new BitSet;
bs
.flip(0, 62)
.flip(29, 35);

let str = bs.toString();

if (str === "111111111111111111111111111000000011111111111111111111111111111") {
console.log("YES!");
}
`

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`javascript
let bs = new BitSet;
bs.setRange(10, 18, 1); // Set a 1 between 10 and 18, inclusive
`

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If you want to store user permissions in your database and use BitSet for the bit twiddling, you can start with the following Linux-style snippet:
`javascript
let P_READ = 2; // Bit pos
let P_WRITE = 1;
let P_EXEC = 0;

let user = new BitSet;
user.set(P_READ); // Give read perms
user.set(P_WRITE); // Give write perms

let group = new BitSet(P_READ);
let world = new BitSet(P_EXEC);

console.log("0" + user.toString(8) + group.toString(8) + world.toString(8));
`

Installation


`
npm install bitset
`

Using BitSet.js with the browser

`html


`

Using BitSet.js with require.js

`html


`

Constructor

The default BitSet constructor accepts a single value of one the following types :

- String
- Binary strings : new BitSet("010101")
- Binary strings with prefix : new BitSet("0b010101")
- Hexadecimal strings with prefix new BitSet("0xaffe")
- Array
- The values of the array are the indices to be set to 1 : new BitSet([1,12,9])
- Uint8Array
- A binary representation in 8 bit form
- Number
- A binary value
- BitSet
- A BitSet object, which get copied over

Functions


The data type Mixed can be either a BitSet object, a String or an integer representing a native bitset with 31 bits.

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Mutable; Sets value 0 or 1 to index ndx of the bitset

int get(ndx)
---
Gets the value at index ndx

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Mutable; Helper function for set, to set an entire range to a given value

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Mutable; Sets a portion of a given bitset to zero

- If no param is given, the whole bitset gets cleared
- If one param is given, the bit at this index gets cleared
- If two params are given, the range is cleared

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Immutable; Extracts a portion of a given bitset as a new bitset

- If no param is given, the bitset is getting cloned
- If one param is given, the index is used as offset
- If two params are given, the range is returned as new BitSet

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Mutable; Toggles a portion of a given bitset

- If no param is given, the bitset is inverted
- If one param is given, the bit at the index is toggled
- If two params are given, the bits in the given range are toggled

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Immutable; Calculates the bitwise complement

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Immutable; Calculates the bitwise intersection of two bitsets

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Immutable; Calculates the bitwise union of two bitsets

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Immutable; Calculates the bitwise xor between two bitsets

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Immutable; Calculates the bitwise difference of two bitsets (this is not the nand operation!)

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Immutable; Clones the actual object

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Returns an array with all indexes set in the bitset

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Returns a string representation with respect to the base

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Calculates the number of bits set

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Calculates the most significant bit (the left most)

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Calculates the number of trailing zeros (zeros on the right). If all digits are zero, Infinity is returned, since BitSet.js is an arbitrary large bit vector implementation.

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Calculates the least significant bit (the right most)

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Checks if the bitset has all bits set to zero

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Checks if two bitsets are the same

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Alternative constructor to pass with a binary string

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Alternative constructor to pass a hex string

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Create a random BitSet with a maximum length of n bits

Iterator Interface

A BitSet object is iterable. The iterator gets all bits up to the most significant bit. If no bits are set, the iteration stops immediately.

`js
let bs = BitSet.Random(55);
for (let b of bs) {
console.log(b);
}
`

Note: If the bitset is inverted so that all leading bits are 1, the iterator must be stopped by the user!

Coding Style

As every library I publish, BitSet.js is also built to be as small as possible after compressing it with Google Closure Compiler in advanced mode. Thus the coding style orientates a little on maxing-out the compression rate. Please make sure you keep this style if you plan to extend the library.

Building the library

After cloning the Git repository run:

`
npm install
npm run build
`

Run a test

Testing the source against the shipped test suite is as easy as

`
npm run test
``

Copyright and Licensing

Copyright (c) 2024, Robert Eisele
Licensed under the MIT license.