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 |
yarn add @thi.ng/rle-pack
let rle = require("@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 = 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);- Karsten Schmidt
© 2017 Karsten Schmidt // Apache Software License 2.0