Bit Smush 🤗

:book: BitSmush

A namespace for binary operations. All otherwise reserved operators for bit manipulation should be contained within. Providing a single lint exception class encapsulation.

SmushMap

The methods smushBits and unSmushBits work given a template of the data offset and length. This template (SmushMap) consists of an array of arrays that contain two numbers - the offset and length.

• Offset is calculated from the right most bit, starting at zero
• Length is number of bits to copy into destination.

Offset index numbering | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |:-:|:-:|:-:|:-:|:-:|:-:|:-:|:-:|

The following SmushMap [[ 5, 2 ], [ 2, 2 ]] with the source data [3, 2] will produce 0b00_11_0_10_0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |:-:|:-:|:-:|:-:|:-:|:-:|:-:|:-:| | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 0 |

A bit-flags style SmushMap could be expressed as [ [6, 1], [5, 1], [3, 1], [2, 1]]. Using the source data of [ENABLED, ENABLED, DISABLED, ENABLED] (aka [1, ,1 ,0, 1]) | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |:-:|:-:|:-:|:-:|:-:|:-:|:-:|:-:| | 0 | 1 | 1 | 0 | 0 | 1 | 0 | 0 |

The following methods smushBits and unSmushBits work using these templates definitions.

smushBits and unSmushBits

Packs or Unpacks multiple number values of specified length (in bits) into or out of a single 8-bit number given a SmushMap template.

const template = [ [6, 1], [5, 3], [1, 2] ]

| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |:-:|:-:|:-:|:-:|:-:|:-:|:-:|:-:| | 0 | X | Y | Y | Y | 0 | Z | Z |

const source = [1, 3, 2]
const expected = 0b0_1_011_0_10 // 0x5A
const outRegister = BitSmush.packBits(template, source)
expect(outRegister).to.equal(expected)

And thus:

const inRegister = 0x5A
const [one, three, two] = BitSmush.unpackBits(template, inRegister)
expect(one).to.equal(1)
expect(two).to.equal(2)
expect(three).to.equal(3)