@thi.ng/rle-pack
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Binary run-length encoding packer w/ flexible repeat bit widths
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# 
[](https://www.npmjs.com/package/@thi.ng/rle-pack)
[](https://mastodon.thi.ng/@toxi)
> [!NOTE]
> This is one of 210 standalone projects, maintained as part
> of the [.ng/umbrella](https://github.com/thi-ng/umbrella/) monorepo
> and anti-framework.
>
> 🚀 Please help me to work full-time on these projects by [sponsoring me on
> GitHub](https://github.com/sponsors/postspectacular). Thank you! ❤️
- [About](#about)
- [Encoding format](#encoding-format)
- [Status](#status)
- [Related packages](#related-packages)
- [Installation](#installation)
- [Dependencies](#dependencies)
- [API](#api)
- [Authors](#authors)
- [License](#license)
## About
Binary [run-length
encoding](https://en.wikipedia.org/wiki/Run-length_encoding)
packer/unpacker with support for customizable input word sizes (1 - 32
bits) and repeat count (run-length) bit sizes (1 - 16 bits). The encoder
uses 4 different repeat group sizes (thresholds) to minimize the number
of bits used to store the run lengths. The range of supported run
lengths is 16 bits (i.e. 65536 repetitions). If a value is repeated more
often than that, the remainder will be encoded using additional RLE
chunks...
### Encoding format
- 32 bits - original number of words
- 5 bits - word size
- 16 bits - 4x RLE repeat group / chunk sizes (in bits)
The default group sizes are: 3, 4, 8, 16, i.e. 8, 16, 256, 65536 repetitions
Then per value:
- 1 bit - encoding flag (1 = RLE encoded, 0 = single occurrence)
- 2 bits - repeat or chunk class ID
- m bits - repeat count or chunk size (if greater than max group size
then split into chunks...)
- n bits - value(s)
## Status
**STABLE** - used in production
[Search or submit any issues for this package](https://github.com/thi-ng/umbrella/issues?q=%5Brle-pack%5D+in%3Atitle)
## Related packages
- [.ng/binary](https://github.com/thi-ng/umbrella/tree/develop/packages/binary) - 100+ assorted binary / bitwise operations, conversions, utilities, lookup tables
- [.ng/bitstream](https://github.com/thi-ng/umbrella/tree/develop/packages/bitstream) - ES6 iterator based read/write bit streams with support for variable word widths
- [.ng/range-coder](https://github.com/thi-ng/umbrella/tree/develop/packages/range-coder) - Binary data range encoder / decoder
## Installation
```bash
yarn add .ng/rle-pack
```
ESM import:
```ts
import * as rle from "@thi.ng/rle-pack";
```
Browser ESM import:
```html
<script type="module" src="https://esm.run/@thi.ng/rle-pack"></script>
```
[JSDelivr documentation](https://www.jsdelivr.com/)
For Node.js REPL:
```js
const rle = await import("@thi.ng/rle-pack");
```
Package sizes (brotli'd, pre-treeshake): ESM: 637 bytes
## Dependencies
- [.ng/bitstream](https://github.com/thi-ng/umbrella/tree/develop/packages/bitstream)
- [.ng/errors](https://github.com/thi-ng/umbrella/tree/develop/packages/errors)
## API
[Generated API docs](https://docs.thi.ng/umbrella/rle-pack/)
```ts
import { encode, decode } from "@thi.ng/rle-pack";
// prepare dummy data
src = new Uint8Array(1024);
src.set([1,1,1,1,1,2,2,2,2,3,3,3,4,4,5,4,4,3,3,3,2,2,2,2,1,1,1,1,1], 512);
// pack data
packed = encode(src, src.length);
packed.length
// 30 => 2.93% of original
// pack with custom word size (3 bits, i.e. our value range is only 0-7)
// and use custom repeat group sizes suitable for our data
alt = encode(src, src.length, 3, [1, 2, 3, 9]);
alt.length
// 20 => 1.95% of original, 66% of default config
// unpack
unpacked = new Uint8Array(decode(alt));
```
## Authors
- [Karsten Schmidt](https://thi.ng)
If this project contributes to an academic publication, please cite it as:
```bibtex
{thing-rle-pack,
title = "@thi.ng/rle-pack",
author = "Karsten Schmidt",
note = "https://thi.ng/rle-pack",
year = 2017
}
```
## License
© 2017 - 2025 Karsten Schmidt // Apache License 2.0