How can I set the carryflag adding two numbers (32bit)

Question

i got two numbers by using read_int, and added two numbers. And finally i checked the EFLAGS (dump_regs).

So, to set carry flag, I tried "4,294,967,295 + 1" but, carry flag didn't set.('CF' didn't show in screen )

What numbers do i need if i want to set carryflag?

    call read_int
    mov ebx, eax

    call read_int
    mov ecx, eax

    mov edx, ebx             ; add the two numbers, edx = ebx - ecx
    add edx, ecx

    mov eax, edx
    call print_int
    call print_nl
    dump_regs 1

And i entered 4294967295 and 1

Answer 1

You can convince yourself of the carry flag getting set, if you run the following code:

call read_int    ;Input say 150
mov ebx, eax
call read_int    ;Input say 180

add al, bl       ;This produces a carry because 150+180=330 DOESN'T FIT the 8-bit register AL

setc al          ;AL becomes 1
movzx eax, al    ;EAX becomes 1
call print_int   ;Show it

Verify with numbers that don't produce a carry:

call read_int    ;Input say 80
mov ebx, eax
call read_int    ;Input say 125

add al, bl       ;This produces NO carry because 80+125=205 DOES FIT the 8-bit register AL

setc al          ;AL becomes 0
movzx eax, al    ;EAX becomes 0
call print_int   ;Show it