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13. Signed Numbers Addition, Cont.

  •  

    INPUTS OUTPUTS
    Asign Bsign CARRY IN CARRY OUT SUMsign OVERFLOW
    0 0 0 0 0 0
    0 0 1 0 1 1
    0 1 0 0 1 0
    0 1 1 1 0 0
    1 0 0 0 1 0
    1 0 1 1 0 0
    1 1 0 1 0 1
    1 1 1 1 1 0

  •  

  • Notice that overflow occurs only when

    • CARRYin ≠ CARRYout

  • or simply

    • V = Cin XOR Cout

  • where V is the overflow signal.

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