Question

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about assembly CF(Carry) and OF(Overflow) flag

I’m trying to see if carry occurs after adding two unsigned dwords.

like this:

       add edx, eax           ; edx will hold the numeric value
       wait                   ; not really needed
       jc bad                 ; jmp to bad if carry bit is set
       jo bad                 ; jmp to bad if overflow bit is set (Yes for signed)

However, neither the overflow flags or carry flags are set accordingly. For testing purposes I do make sure that the addition will result in a value too big for 32bit reg. (after adding, the values wrap around)

How do I check if the two numbers added together will result in overflow?

Answer 1

The overflow is used for signed addition and subtraction.

You should look at just the carry flag for unsigned addition and subtraction.