rlf     GPIO,w          ;      W = 0DC0BAxc   x = old GP0,
        movwf   SWITCH          ; SWITCH = 0DC0BAxc   c = old carry
        rlf     SWITCH,f        ; SWITCH = DC0BAxc0
        movlw   0x18            ;      W = 00011000
        andwf   SWITCH,w        ;      W = 000BA000
        addwf   SWITCH,f        ; SWITCH = DCBA0xc0

  Obviously, two more instructions can "clean" the spurious bits out.
--
  Cheers,
        Paul B.