I think your premise is wrong, just do the addition like so and throw away the carry out (which by itself is actually the overflow detection in logic terms).
| 1 1 0 = -2
+ | 1 1 0 = -2
------------
1 | 1 0 0 = -4
I think your premise is wrong, just do the addition like so and throw away the carry out (which by itself is actually the overflow detection in logic terms).
| 1 1 0 = -2
+ | 1 1 0 = -2
------------
1 | 1 0 0 = -4