Thread: Emulating x86 Instructions

Hello,

I'm trying to translate some x86 assembly language into C so I can better understand what it's doing, however I can't really work out how best to deal with the "Add With Carry" (ADC) and "Subtract With Borrow" (SBB) instructions. In this code, they always come immediately after an ADD/SUB instruction performed on the next word along in memory, so I would presume that the one instruction affects the other, particularly when I'm seeing things like:-

Code:

sub [BX+(blah + 2)], 0Ah
sbb [BX+blah], 0

Which to my mind, the second instruction does nothing.

What's the C equivalent?

They handle overflow / underflow when manipulating values which are wider than registers.

14
19 +
33

4 and 9 you add and the result is 3 (but there's a carry)
1 and 1 you "add with carry" and you get 3 as well
Hence the result.