Complete the following sentences for computing the Overflow flag for signed numbers $(3)$

When adding signed numbers represented in two's complement, overflow occurs only in two scenarios:

adding two positive numbers but..

adding two negative numbers but $..$

Similarly, when subtracting signed numbers, overflow occurs in two scenarios:

subtracting a positive number from a negative number but $..$

subtracting a negative number from a positive number but $..$

Rewrite the following code by reducing the number of registers usage only $3.(4)$