You might be interested this one.
No no no, I don't want to look at someone else's code.
Ok I had a peek. He called his object the same name as mine - "TuInt128". I didn't copy, honest!
I've already scratched out an outline of my code, it's much less ambitious than that project. Just methods for basic conversion like ToString, FromString and few other initialization methods, and then the basic arithmetic stuff like Add, Neg, Div Mult and Compare. A couple of hundred lines at most. The only thing I haven't already scratched out is some power/modulo stuff I'll probably add later.
This is just a simple project I set myself to get back into programming. I used to program in Pascal back in the turbo pascal days, but haven't done much recently. And last time I tried to optimize asm code it was on and AMD k6-2, Haha, so that's how far out of touch I am.
Also wanted to learn a bit about x64 asm. But don't worry I'm not under any illusions, I know that I'm out of my depth when it comes to optimizing. This is just a simple learning project.