Ray Gardiner wrote:
> ; 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,

Initial conditions: high = 00 , mid = 00 , low = 0xFF

high    mid     low
0x00    0x00    0xFF
0xFF    0x00    0xFF
0xFF    0xFF    0xFF
0xFF    0xFF    0xFE

Result: high = 0xFF , mid = 0xFF , low = 0xFE

WBR Dmitry.