clownlzss is a lightweight, minimalist, graph-based LZSS framework. Also included are a collection of compressors which utilise the framework.

Formats supported by the supplied utilities include:

• Kosinski - a compression format common to first-party Sega Mega Drive games

• Saxman - a format used by Sonic the Hedgehog 2, to compress its sound engine and music data (is actually a lightly-modified version of Haruhiko Okumura's 1989 LZSS format)

• Chameleon - a format that saw use in Kid Chameleon and Sonic the Hedgehog 2's "Nick Arcade" prototype

• Rocket - a format used by Rocket Knight Adventures

• Rage - a format used by Streets of Rage 2 (is actually RLE, not LZSS)

• Kosinski+ - a modified version of Kosinski developed by the Sonic ROM-hacking community, which optimises the format for the Mega Drive's CPU, improving decompression speed at no cost to compression ratio

• Faxman - a modified version of Saxman designed to produce smaller files when used to compress SMPS music data

• Comper - another community-developed format, which is designed from the ground up with a focus on decompression speed on the Motorola 68000. This comes at a significant cost to compression ratio

clownlzss utilises graph theory to perform optimal compression: naive "greedy algorithm" compressors prefer to compress the longest runs possible, but this does not guarantee the best compression ratio. Graph-based compressors resolve this by creating an "LZSS graph" - a weighted directed acyclic graph where each node is a value in the uncompressed file, and each edge is an LZSS match. By using a shortest-path algorithm, this graph can be used to compute the ideal combination of matches needed to produce the smallest file.

This project is under the 0BSD licence.