# bit-twiddle

Bit twiddling hacks for JavaScript

``npm install bit-twiddle``

# bit-twiddle

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

http://graphics.stanford.edu/~seander/bithacks.html

# Install

Via npm:

``````npm install bit-twiddle
``````

# Functions

## `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

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