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• About
  • Simple RLE
  • Binary encoding
    • Encoding format
    • Code example
• Status
• Related packages
• Installation
• Dependencies
• API
• Authors
• License

About

The package provides two approaches for Run-length encoding/decoding:

Simple RLE

The naive approach operates on arrays of arbitrary values and supports user-defined predicates to determine if a consecutive input values are equal (i.e. repeated). By default uses === strict comparison.

import { encodeSimple, decodeSimple } from "@thi.ng/rle-pack";

const src = [..."aaaaaabbbbaaaxyxxx"];

const encoded = encodeSimple(src);
console.log(encoded);
// ["a", 6, "b", 4, "a", 3, "x", 1, "y", 1, "x", 3]

const decoded = decodeSimple(encoded);
console.log(decoded);
// ["a", "a", "a", "a", "a", "a", "b", "b", "b", "b", "a", "a", "a", "x", "y", "x", "x", "x"]

Binary encoding

Binary 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)

Code example

import { encodeBinary, decodeBinary } from "@thi.ng/rle-pack";

// prepare dummy data
const 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
const packed = encodeBinary(src, src.length);
console.log(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
const alt = encodeBinary(src, src.length, 3, [1, 2, 3, 9]);
console.log(alt.length);
// 20 => 1.95% of original, 66% of default config

// unpack
const unpacked = decodeBinary(alt);
console.log(unpacked.length);

Status

STABLE - used in production

Search or submit any issues for this package

Related packages

• @thi.ng/binary - 100+ assorted binary / bitwise operations, conversions, utilities, lookup tables
• @thi.ng/bitstream - ES6 iterator based read/write bit streams with support for variable word widths
• @thi.ng/range-coder - Binary data range encoder / decoder

Installation

yarn add @thi.ng/rle-pack

ESM import:

import * as rle from "@thi.ng/rle-pack";

Browser ESM import:

<script type="module" src="https://esm.run/@thi.ng/rle-pack"></script>

JSDelivr documentation

For Node.js REPL:

const rle = await import("@thi.ng/rle-pack");

Package sizes (brotli'd, pre-treeshake): ESM: 802 bytes

Dependencies

• @thi.ng/api
• @thi.ng/bitstream
• @thi.ng/errors

Note: @thi.ng/api is in most cases a type-only import (not used at runtime)

API

Generated API docs

Authors

• Karsten Schmidt

If this project contributes to an academic publication, please cite it as:

@misc{thing-rle-pack,
  title = "@thi.ng/rle-pack",
  author = "Karsten Schmidt",
  note = "https://thi.ng/rle-pack",
  year = 2017
}

License

© 2017 - 2026 Karsten Schmidt // Apache License 2.0