overflow condition

Question

We consider the addition of two 2’s complement numbers bn-1bn-2...b0 and an-1an-2...a0. A binary adder for adding unsigned binary numbers is used to add the two numbers. The sum is denoted by cn-1cn-2...c0 and the carry-out by cout. Which one of the following options correctly identifies the overflow condition?

Answer 1

Overflow condition is meant for range exceeding condition of a signed number..

So this happens in 2's complement number addition if either there is a carry in to the MSB of the result or carry out of the MSB of the result .But both should not happen at the same time..

So this scenario can be represented by XOR of Cout (Carry out of MSB) and C_n-1 (Carry in to the MSB)..

Hence C) is the correct answer..

Comments

but Cn-1 is not carry from MSB it is sum bit of an-1 and bn-1

Answer 2

https://gateoverflow.in/1815/gate2006-39

https://gateoverflow.in/65133/overflow-conditions

http://teaching.idallen.com/dat2343/10f/notes/040_overflow.txt