Actually reading the Lua mailing list post http://lua-users.org/lists/lua-l/2010-03/msg00305.html, referenced in the linked text might help:

> For pidigits I'm comparing the pure JS and Lua programs, not the GMP bindings.

I'm comparing these two:

http://shootout.alioth.debian.org/u32/program.php?test=pidig...

http://shootout.alioth.debian.org/u32/program.php?test=pidig...

Both are written in pure Lua and JavaScript and do not use a C binding.