Hi,

> I'm working on a project where ROM space is at an abolute minimum,
> and I've tried every trick I can think of to squeeze everything in.
> Unfortunately, I'm still a bit over the limit.
>
> Has anyone got a tight routine to subtract a 16 bit number from a 32
> bit number. The result is placed back in the 32 bit number.
>
> TIA
>
> Tony
>
What about:

;Subtract 16 bit number in A1,A0 from 32 bit number in B3,B2,B1,B0
;Answer is left in B3,B2,B1,B0

    movf    B0, W
    subwf   A0, F
    movf    B1, W
    skpc
     incfsz B1, W
     subwf  A1, F
    movlw   0FFh
    skpc
     addwf  A2, F
    skpc
     addwf  A3, F

Niki