Hi,
Perhaps if you would elaborate a bit on the actual
formula you intend to use I can give some hints.

Signed/unsigned is fairly trivial
unless you mix data of variable size and signed/unsigned
then it starts to get a bit tricky :)

We have had some disscussions about signed/unsigned on the list
check the archives.

But a short re-cap ( signed math ):

Top bit set (msbit) = Value is negative
Top bit clear (msbit) = Value is positive

For addition/subtraction you need no special routines,
unless there are possibilities for overflow.

To 'convert' from negative to positive ( or the other way around ):

;++++++++++++
;
; NORM_16 - Normalises a 16 bit variable ( i.e make two's complement )
; argument must point to most significant byte, arg16+1 is lsb

NORM_16 MACRO   ARG_16
        ; first make one's complement
        COMF    LOW(ARG_16+1),F
        COMF    LOW(ARG_16),F
        ; then add one to form two's complement
        MOVLW   1
        ADDWF   LOW(ARG_16+1),F
        SKPNC
        ADDWF   LOW(ARG_16),F
        ENDM

/Tony

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