Midway never released the source code to Doom 64 which means that the code unique to Doom 64 EX has been written from scratch with the aid of a disassembler to insure accuracy in certain areas. It uses the GPL’ed source code of Doom 2 released by id Software. Does Doom 64 EX use any source code from the original game? Though technically it is a PC-port of the original game, it is not a classified as a source port.