I've started working on an AMD64 version of longest_match I'm using Microsoft Visual Studio 2005 beta 1 and ml64 (from ftp://ftp.sandpile.org/ml64.zip ) http://gilles.vollant.free.fr/asmamd64.zip with my visual studio 2005 beta project http://gilles.vollant.free.fr/testzl_asmamd64.zip