I think SBB emulation is broken.

[AndreasPK]

By the spec it's defined as DEST ← (DEST – (SRC + CF));

But I think it's implemented as DEST ← (DEST – SRC + CF);

Reproducible with this snippet.

    MOV EAX, 10
    MOV EBX, -1 ; 
    ADD EBX, 1 ; CF = 1
    SBB EAX, 0 ; EAX = (EAX - (0 + CF)) = EAX - 1 = 9
    ; EAX should be 9, it is 11

[Kobzol]

Hi, yes, you're right, as I learned recently, the handling of the carry flag is broken for subtraction. A proper fix will require a reimplementation of the ALU logic and number representation. I haven't gotten to it yet, but I'll try to do it once I have some more time. And of course I would welcome PRs 😅.