If I have
0010 1101
0110 1111
____+
1001 1100
Is it overflow? because the sign of the first digit becomes 1 and 1 represents negative? I am very weak in binary.
What if you add
1111 1111
1111 1111
___+
1111 1110
with carryout 1 that is not an overflow? because 1111 1110 represents -2?
Thanks for helping!
It depends on how you are treating your value - is it signed or unsigned. If it is unsigned binary, than it is not overflow. If it is signed one, than overflow did occure.
I guess we are talking about signed values, than basicly, overflow is when value change its sign due to binary arithmetic operation which result exceeds max-min range.
If you are using a plain binary representation without sign, it is not an overflow
0010 1101->45
0110 1111->111
45+111 = 156. You can operate in the range [0, 255] then it is not an overflow.
If you are using the two's complement you have the range from -128 to 127, having only one representation of 0. Then it is an overflow because 156 is out of the range [-128, 127]
You can not just use the first bit to represent the sign because then you have 10000000 and 00000000 representing 0 and -0. The you should use two's complement to operate with negative numbers.
