I'm sorry but the game was not "ported" to the Amiga. This is completely wrong. It was made and designed on the Amiga by Eric Chahi himself. The PC version is a port. I know because I got the Amiga version right when it was out back in the days and it was the first one, plus I watched numerous documentaries showing Chahi working on his Amiga when making the game.

So if you want to look at the original source code (or at least understand how it may have worked) it would be wiser to decompile the Amiga binaries.