Gate2017 cs Q29
- Option : C
- Explanation : Overflow flag indicates an over flow condition for a signed operation. Some points to remember in a signed operation: * MSB is always reserved to indicate sign of the number. * Negative numbers are represented in 2’s – complement. * An overflow results in invalid operation. 2's complement overflow rules: * If the sum of two positive numbers yields a negative result, the sum has- overflowed. * If the sum of two negative number yields a positive result, the sum has overflowed. * Otherwise, the sum has not overflowed. Overflow for signed numbers occurs when the carry-in into the MSB (most significant bit) is not equal to carry-out. Conveniently, an XOR-operation on these two bits can quickly determine if an overflow condition exists. Therefore, ((A7.B7) ⊕ S7 = (A7.B7.S7 + A7.B7.S7) = 1 has overflowed.
