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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.

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 1.4.1  6910729 (24,75%)

The output is fully compatible with the original aPLib by Jørgen Ibsen.


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

Some projects that use apultra for compression:

Also of interest:


  • 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.