On Wed, 28 Nov 2001, Vasile Surducan wrote:

> On Tue, 27 Nov 2001, Drew Vassallo wrote:
>
> > >Compare two 16 Bit numbers, require flag when one greater than the other?
> > >
> > >Anyone have the solution?
> >
> > No, but I'm sure you can find it here:
> >
> > http://www.piclist.com/techref/microchip/compcon.htm#16_bit
>
>
>   or here: http://www.geocities.com/vsurducan/electro/PIC/lib.html

I've been looking at comparisons lately. In fact I've been looking at them
too much and am starting to get sick of it (but that's another story).

I saw your page Vasile and noticed that it can be dramatically
streamlined if your're willing to change the interface ever so slightly.

; unsigned char compare_lt_eq_gt(unsigned int a, unsigned int b)
;
; compare two integers. return 0 if they're equal, 1 if a>b, or 2 if a<b
;

    movf   HIGH(b)
    subwf  HIGH(a)     ; first upper bytes
    skpnc
     retlw 1           ; b is less than a

    skpnz
     retlw 2           ; a is less than b

    movf   LOW(b)
    subwf  LOW(a)      ; compare lower bytes

    skpnc
     retlw 1           ; b is less than a

    skpnz
     retlw 2           ; a is less than b

    retlw  0           ; a and b are equal

However if you want to return the value in a register (like the example on
your web page) then:

    clrf   result

    movf   HIGH(b),w
    incfsz result,f    ;put 1 into result, note skip will not happen!
     subwf HIGH(a),w   ;compare high bytes

    skpnc
     return            ; b is less than a, return 1

    rlf    result,f    ; result == 2
    skpz
     return            ; a is less than b, return 2

    movf   LOW(b),w
    decfsz result,f    ;put 1 into result again
     subwf LOW(b),w

    skpnc              ; b is less than a, return 1
     return

    bcf   result,0    ; result now = 0, assume a == b
    skpnz
     bsf  result,1    ; result now = 2,  a is less than b

    return

A little obscure perhaps, but gets the job done. Note, this won't work on
the 18c core, but then again on the 18c core you'd make use of the addwfc
instruction.


Scott

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads