Overflow: 2C

V = ck-1 XOR ck-2

Why does this work?

Case 1: 0 carried in, 1 carried out

This occurs only when both xk-1 and yk-1 are 1, but then sk-1 is 0,

so the result is non-negative even though both x and y are negative.

Case 2: 1 carried in, 0 carried out

This occurs only when both xk-1 and yk-1 are 0, but then sk-1 is 1,

so the result is negative even though both x and y are non-negative.

Adder with overflow detection