Thing-rle-pack NPM

thi.ng/rle-pack

Overview

Binary run-length encoding packer/unpacker w/ flexible repeat bit widths. Written in TypeScript, distributed in ES6.

Encoding format:

32 bits - original size in bytes (header)

Then per value:

1 bit - encoding flag (1 = RLE encoded, 0 = single occurrence)
8 bits - value

The following is only used for repeated values:

2 bits - repeat class
3/4/8/16 bits - repeat count - 1 (if > 0x10000 then split into chunks...)

Repeats	Original (bits)	RLE (bits)	Saving (bits)	Ratio
1	8	1+8	-1	1.125
2	16	1+8+2+3	2	0.875
3	24	1+8+2+3	10	0.583
4	32	1+8+2+3	18	0.438
8	64	1+8+2+3	50	0.219
9	72	1+8+2+4	57	0.208
16	128	1+8+2+4	113	0.117
17	136	1+8+2+8	117	0.14
256	2048	1+8+2+8	2029	0.0093
257	2056	1+8+2+16	2029	0.013
512	4096	1+8+2+16	4069	0.0066
1024	8192	1+8+2+16	8165	0.0033
65536	524288	1+8+2+16	524261	0.000051

Installation

npm i thing-rle-pack

API

let rle = require("thing-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 = rle.encodeBytes(src);
// Uint8Array [0,0,4,0,128,96,63,240,18,64,135,3,20,16,32,88,32,96,98,129,14,2,72,6,3,196]
 
packed.length
// 26 => 2.5% of original

// unpack
dest = rle.decodeBytes(packed);