Source releases aren't compressed.

These links list files as "tgz" with a size of 150k.

 "http://tidy.sourceforge.net/src/tidy_src.tgz"
 "http://tidy.sourceforge.net/src/old/"

Gzip kept complaining of a bad header, so I looked at the files with
Emacs in hexl-mode and they are straight tar file.

fwiw,
Bill Pringlemeir.