bit-twiddle

What is bit-twiddle?

The bit-twiddle npm package provides a collection of functions for performing common bitwise operations in JavaScript. It is useful for tasks that require low-level manipulation of binary data, such as graphics programming, cryptography, and performance optimization.

What are bit-twiddle's main functionalities?

Set a bit

This feature allows you to set a specific bit in a number. In the example, the second bit (index 1) of the binary number 0000 is set, resulting in 0010.

const bt = require('bit-twiddle');
let num = 0b0000;
num = bt.setBit(num, 1);
console.log(num.toString(2)); // Output: 10

Clear a bit

This feature allows you to clear a specific bit in a number. In the example, the third bit (index 2) of the binary number 1111 is cleared, resulting in 1011.

const bt = require('bit-twiddle');
let num = 0b1111;
num = bt.clearBit(num, 2);
console.log(num.toString(2)); // Output: 1011

Toggle a bit

This feature allows you to toggle a specific bit in a number. In the example, the second bit (index 1) of the binary number 1010 is toggled, resulting in 1000.

const bt = require('bit-twiddle');
let num = 0b1010;
num = bt.toggleBit(num, 1);
console.log(num.toString(2)); // Output: 1000

Check if a bit is set

This feature allows you to check if a specific bit in a number is set. In the example, the second bit (index 1) of the binary number 1010 is checked, and it is set.

const bt = require('bit-twiddle');
let num = 0b1010;
let isSet = bt.isBitSet(num, 1);
console.log(isSet); // Output: true

Count the number of set bits

This feature allows you to count the number of set bits (1s) in a number. In the example, the binary number 1011 has three set bits.

const bt = require('bit-twiddle');
let num = 0b1011;
let count = bt.popCount(num);
console.log(count); // Output: 3

Other packages similar to bit-twiddle

bitwise

The bitwise package provides a comprehensive set of bitwise operations for JavaScript. It includes functions for bit manipulation, bitwise arithmetic, and more. Compared to bit-twiddle, bitwise offers a broader range of functionalities and is more actively maintained.

bitset

The bitset package allows for the manipulation of large sets of bits. It provides a BitSet class that supports various bitwise operations. While bitset is more focused on handling large bitsets efficiently, bit-twiddle is more about providing simple, low-level bitwise operations.

bitwise-operator

The bitwise-operator package offers a collection of bitwise operations similar to bit-twiddle. It includes functions for setting, clearing, toggling, and checking bits. However, bitwise-operator is less popular and less frequently updated compared to bit-twiddle.

README

bit-twiddle

This is a collection of miscellaneous bit twiddling hacks ported to JavaScript, mostly taken from here:

• Stanford Bit Twiddling Hacks

Install

Via npm:

npm install bit-twiddle

API

sign(v)

Computes the sign of the integer v. Returns:

• -1 if v < 0
• 0 if v === 0
• +1 if v > 0

abs(v)

Returns the absolute value of the integer v

min(x,y)

Computes the minimum of integers x and y

max(x,y)

Computes the maximum of integers x and y

isPow2(v)

Returns true if v is a power of 2, otherwise false.

log2(v)

Returns an integer approximation of the log-base 2 of v

log10(v)

Returns log base 10 of v.

popCount(v)

Counts the number of bits set in v

countTrailingZeros(v)

Counts the number of trailing zeros.

nextPow2(v)

Rounds v up to the next power of 2.

prevPow2(v)

Rounds v down to the previous power of 2.

parity(v)

Computes the parity of the bits in v.

reverse(v)

Reverses the bits of v.

interleave2(x,y)

Interleaves a pair of 16 bit integers. Useful for fast quadtree style indexing. (See wiki: http://en.wikipedia.org/wiki/Z-order_curve )

deinterleave2(v, n)

Deinterleaves the bits of v, returns the nth part. If both x and y are 16 bit, then it is true that:

deinterleave2(interleave2(x,y), 0) === x
deinterleave2(interleave2(x,y), 1) === y

interleave3(x,y,z)

Interleaves a triple of 10 bit integers. Useful for fast octree indexing.

deinterleave3(v, n)

Same deal as deinterleave2, only for triples instead of pairs

nextCombination(x)

Returns next combination ordered colexicographically.

Acknowledgements

Code is ported from Sean Eron Anderson's public domain bit twiddling hacks page. http://graphics.stanford.edu/~seander/bithacks.html JavaScript implementation (c) 2013 Mikola Lysenko. MIT License