https://github.com/johntalton/bitsmush
Pack and Unpack bits from a byte
https://github.com/johntalton/bitsmush
bit byte pack smush
Last synced: 11 months ago
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Pack and Unpack bits from a byte
- Host: GitHub
- URL: https://github.com/johntalton/bitsmush
- Owner: johntalton
- License: mit
- Created: 2021-03-16T00:00:24.000Z (over 5 years ago)
- Default Branch: main
- Last Pushed: 2024-05-05T13:41:33.000Z (about 2 years ago)
- Last Synced: 2025-07-26T23:12:12.445Z (11 months ago)
- Topics: bit, byte, pack, smush
- Language: JavaScript
- Homepage:
- Size: 7.81 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# Bit Smush 🤗
[](https://www.npmjs.com/package/@johntalton/bitsmush)
[](https://www.npmjs.com/package/@johntalton/bitsmush)
## :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.
```javascript
const template = [ [6, 1], [5, 3], [1, 2] ]
```
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|:-:|:-:|:-:|:-:|:-:|:-:|:-:|:-:|
| 0 | `X` | `Y` | `Y` | `Y` | 0 | `Z` | `Z` |
```javascript
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:
```javascript
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)
```