$-$ Design a $4-$bit$-$by$-4-$bit including sign $($A and B$)$ simple calculator, as shown

in the figure:

The calculator performs addition, subtraction, XOR and absolute operations

according to the values of the select lines $($Co to C$3).$ The following table

shows these operations:

C$1$ Co F

$00$ A$+$B

$01$ A$$B