[bitwave]

reminds me of zpaq [1]. It is an public domain compression tool, which save the decompression algorithm as IR into the compressed archive. It is written by Matt Mahoney, best known for the PAQ archiver series.

[1]: http://mattmahoney.net/dc/zpaq.html

[daniel_rh]

It has some similarities to zpaq, especially with the -mixing=2 parameter. With -mixing=2, DivANS runs 2 models to estimate the upcoming nibble or byte and dynamically chooses the best model based on past performance. One of the two models is good for more diffuse patterns and the other is good for more pronounced patterns. I believe the paq technology runs dozens of models and uses similar but slightly more advanced models to mix between them. This results in excellent compression but means you have to evaluate those models to decompress the data when you need it later.

Without -mixing=2 (eg for the results present in the blog post), DivANS actually relies on a static determination about which models to use in which situations, serialized into the file in the mixing map. It only ever evaluates a single model per nibble.

The idea of mashing up the intermediate representation with a bunch of different compressors isn't present in zpaq as far as I know, but the spirit of the idea is similar, but on a per-bit level, rather than on the IR level.

[bitwave]

Big thanks for the clarification.