;
; 24 bit decrement
;                               ; test 1     test2
;                               ;            underflow from zero
;
        MOVF    HIGH,W          ; FF FF 01   00 00 00
        SKPNZ                   ;
        DECF    HIGH,F          ; skip       FF 00 00
        MOVF    MID,W           ;
        SKPNZ                   ;
        DECF    MID,F           ; skip       FF FF 00
        DECF    LOW,F           ; FF FF 00   FF FF FF

;       7 cycles, uses W,
;

Sorry if this solution has already been posted, I have been
otherwise occupied!

--
Ray Gardiner ray@hdc.com.au