mIRC 6.1 added two new identifiers - $compress() and $decompress(), but not many details were given.

What compression algorithm is used for these?
LZW (unlikely, patented by Unisys)?
BZIP2 (unlikely, as it prefers really large files)?
Deflate (i.e. zlib)?

Seeing that the "Acknowledgements" page doesn't mention any other lib than zlib, I would assume zlib is used for $compress() too.