Hi,
I while ago I posted an request for 24x24 =3D 48 and
48/24 =3D 24. Lacking replies ( apart from Nikolai's
pseudo code ) I had to 'make' them myself. Not particulary
hard, just tedious :).
Anyway had some time during the latest days to start hammer on it
and here you have the 24x24 =3D 48 bit routine. I *think* it works
( atleast on the values tested so-far ) but dont take my word on it:


;
***********************************************************************
; MULTTIPLY_24x24 - Routine to mutltiply two 24 bit numbers =

; result in 48 bits !
; Format:       Ram =3D MSB, Ram+2 =3D LSB ( for 24 bit variable ) ( little
endian ? )
; Ram used: Multiplier, Multipland 3 bytes each ( 24 bits ) =

;           Product 6 bytes ( 48 bits ) =

;           BitCount 1 byte for loop counting
;
; Multiplier is zero at exit ( destroyed )
; Multipland is preserved
; Product holds result
;
; Probably more efficient to use Ram =3D LSB, Ram+2 =3D MSB ( big endian =
? )
; According to helpful hints from Nikolai, however my requirements
; dictated the used format.
;
MULTIPLY_24x24
        ; preload values to test
        MOVLW   0xAB
        MOVWF   Multipland
        MOVLW   0xCD
        MOVWF   Multipland+1
        MOVLW   0xEF
        MOVWF   Multipland+2

        MOVLW   0x98
        MOVWF   Multiplier
        MOVLW   0x76
        MOVWF   Multiplier+1
        MOVLW   0x54
        MOVWF   Multiplier+2

        ; these values should generate the reply =3D 0x6651AF33BC6C =


        CLRF    Product         ; clear destination
        CLRF    Product+1
        CLRF    Product+2
        CLRF    Product+3
        CLRF    Product+4
        CLRF    Product+5

        =

        MOVLW   23
        MOVWF   BitCount        ; number of bits
        CLRC                    ; make sure the carry is initially
cleared

ADD_LOOP_24x24
        ; note carry assummed to be zero !
        =

        RLF     Multiplier+2,F  ; up shift multiplier one bit
        RLF     Multiplier+1,F
        RLF     Multiplier,F

        BTFSS   STATUS,C        ; if carry is set we must add multipland
to the product
          GOTO  SKIP_LOOP_24x24 ; nope, skip this bit
                =

        MOVF    Multipland+2,W  ; get LSB of multiplicand
        ADDWF   Product+5,F     ; add it to the lsb of the product
  =

        MOVF    Multipland+1,W  ; middle byte
        BTFSC   STATUS,C        ; check carry for overflow
        INCFSZ  Multipland+1,W  ; =

        ADDWF   Product+4,F     ; handle overflow
        =

        MOVF    Multipland,W    ; MSB byte
        BTFSC   STATUS,C        ; check carry
        INCFSZ  Multipland,W
        ADDWF   Product+3,F     ; handle overflow

        ; carry propagation, if set then make sure if 'follows' through
        =

        MOVLW   0x01            ; preload with 1
        BTFSC   STATUS,C        ; check carry for overflow
        ADDWF   Product+2,F     ; add one to next byte

        BTFSC   STATUS,C        ; check carry for overflow
        ADDWF   Product+1,F     ; add one to next byte

        BTFSC   STATUS,C        ; check carry for overflow
        ADDWF   Product,F       ; add one to next byte
        =


SKIP_LOOP_24x24
        ; shift and prepare for next bit

        ; note Carry is always assumed to be zero here !
        ; should be handled by carry propagation above.
        =

        RLF     Product+5,F
        RLF     Product+4,F
        RLF     Product+3,F
        RLF     Product+2,F
        RLF     Product+1,F
        RLF     Product,F
        ; note carry should always be zero here ( else overflow ? )
        ; affects rotate at the beginning of ADD_LOOP_24x24
        DECFSZ  BitCount,F
        GOTO    ADD_LOOP_24x24
        NOP
        NOP
        RETURN

Use at will/risk/leisure/etc.
Oh..pic-code on the pic-list what will come next ;)

/Tony


Tony K=FCbek, Flintab AB            =

=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=
=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=
=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2
E-mail: tony.kubek@flintab.com
=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=
=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2=
=B2=B2=B2=B2=B2=B2=B2=B2=B2=B2

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