Question

In the following code, the value in AL is intended to be a signed byte. Explain how the Overflow flag helps, or does not help you, to determine whether the final value in AL falls within a valid signed range. mov al,-1 add al,130

Answer 1

Overflow flag helps here in pointing out that arithmetic flow has occurred as the result or final value in AL is outside the valid range.

Step-by-step explanation:

Lets observe the given assembly language code:

mov al,-1

add al,130

The first line moves or copies the value -1 to AL.

The second statement performs arithmetic operation i.e addition and adds 130 to the value stored in AL which is - 1

So the result is 130 + (-1) = 129

Range of a signed integer which is of 1 byte is -128 to 127 and the range of positive signed integer is exceeding 127 (as it is 129).

So this is outside the signed range. So this results in an overflow

Overflow flag works with signed numbers is set to indicate this error that the result is too big to fit in AL. The overflow flag is set here as the result 129 is too big and is out of valid signed range.