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Free open-source compressor for apLib with 5-7% better ratios
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VS2017 Initial commit Nov 3, 2019

apultra -- a new, opensource optimal compressor for the apLib format

apultra is a command-line tool and a library that compresses bitstreams in the apLib format.

The tool produces files that are 5 to 7% smaller on average than appack, the apLib compressor. Unlike the similar cap compressor, apultra can compress files larger than 64K (for files smaller than 64K, cap compresses 0.05% better on average).

apultra is written in portable C. It is fully open-source under a liberal license. You can continue to use the regular apLib decompression libraries for your target environment. You can do whatever you like with it.

Example compression with vmlinux-5.3.0-1-amd64

original       27923676 (100,00%)
appack         7370129 (26,39%)
gzip 1.8       7166179 (25,66%)
apultra 1.0.6  6910794 (24,75%)


  • cap by Sven-Åke Dahl.
  • Charles Bloom's compression blog.
  • LZ4 by Yann Collet.
  • spke for help and support


  • The apultra code is available under the Zlib license.
  • The match finder (matchfinder.c) is available under the CC0 license due to using portions of code from Eric Bigger's Wimlib in the suffix array-based matchfinder.
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