please dont rip this site

PIC Microcontoller Math Method

24x24 multiplication

from Nikolai Golovchenko


Multiplier EQU Product+3  ;3 bytes shared with Product's
                          ;less significant bytes (+3..5)

        ; 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 = 0x6651AF33BC6C

;24 x 24 Multiplication
; Multiplier - 3 bytes (shared with Product)
; Multiplicand - 3 bytes (not modified)
; Bitcount
; Product - 6 bytes

        CLRF    Product         ; clear destination
        CLRF    Product+1
        CLRF    Product+2

        MOVLW   D'24'
        MOVWF   BitCount        ; number of bits

        RRF     Product+3,F     ; shift out to carry
        RRF     Product+4,F     ; next multiplier bit
        RRF     Product+5,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+2,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  ; if carry set we add one to the source 
        ADDWF   Product+1,F     ; and add it  (if not zero, in
                                ; that case mulitpland = 0xff->0x00 )
        MOVF    Multipland,W    ; MSB byte
        BTFSC   STATUS,C        ; check carry
        INCFSZ  Multipland,W
        ADDWF   Product,F       ; handle overflow

        ; note carry contains most significant bit of
        ; addition here

        ; shift in carry and shift out
        ; next multiplier bit, starting from less
        ; significant bit

        RRF     Product,F
        RRF     Product+1,F
        RRF     Product+2,F
        RRF     Product+3,F
        RRF     Product+4,F
        RRF     Product+5,F

        DECFSZ  BitCount,F
        GOTO    ADD_LOOP_24x24


file: /Techref/microchip/math/mul/24x24b-tk.htm, 3KB, , updated: 2010/3/30 08:18, local time: 2024/6/24 10:44,

 ©2024 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?
Please DO link to this page! Digg it! / MAKE!

<A HREF=""> PIC Microcontoller Math Method - 24x24 multiplication</A>

After you find an appropriate page, you are invited to your to this massmind site! (posts will be visible only to you before review) Just type a nice message (short messages are blocked as spam) in the box and press the Post button. (HTML welcomed, but not the <A tag: Instead, use the link box to link to another page. A tutorial is available Members can login to post directly, become page editors, and be credited for their posts.

Link? Put it here: 
if you want a response, please enter your email address: 
Attn spammers: All posts are reviewed before being made visible to anyone other than the poster.
Did you find what you needed?


Welcome to!


Welcome to!