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linuxassemblyx86-64fasmlogical-and

Logical AND implementation in x86_64 Linux assembly

I'm trying to implement logical NOT and logical AND in assembly, I did logical NOT already using x < 1 but I can't think of how to implement AND, I can use binary and but that's broken for negative numbers (it assumes -1 is true) and it doesn't make any sense when NOT obviously works because -1 < 1 would return 1

So I'm confused, how could I do it, any known implementation which I could use? I can't find it, been looking for a while

Solution

  • The standard solution is to implement a && b as

    if (a)
    return (b);
else
    return (0);

    i.e. use a conditional jump. On sufficiently new x86, you can also use a cmov instruction like this:

    ; assumes input in eax and ebx
mov ecx, eax    ; ecx = A
test ebx, ebx   ; B?
cmovnz ecx, ebx ; ecx = A ? B : A