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@thi.ng/rle-pack

@thi.ng/rle-pack

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This project is part of the @thi.ng/umbrella monorepo.

About

Binary run-length encoding packer/unpacker w/ 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

data layout

  • 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)

Installation

yarn add @thi.ng/rle-pack

Dependencies

API

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.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 = rle.encode(src, src.length, 3, [1, 2, 3, 9]);
alt.length
// 20 => 1.95% of original, 66% of default config

// unpack
unpacked = new Uint8Array(rle.decode(alt));

Authors

  • Karsten Schmidt

License

© 2017 - 2018 Karsten Schmidt // Apache Software License 2.0

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