PIC Microcontoller Math Method

32 bits by 16 by Peter Hemsley

divide movlw 32      ; 32-bit divide by 16-bit
       movwf bitcnt
       clrf remdrH   ; Clear remainder
       clrf remdrL

dvloop clrc          ; Set quotient bit to 0
                     ; Shift left dividend and quotient
       rlf divid0    ; lsb
       rlf divid1
       rlf divid2
       rlf divid3    ; lsb into carry
       rlf remdrL    ; and then into partial remainder
       rlf remdrH

       skpnc         ; Check for overflow
       goto subd
       movfw divisH  ; Compare partial remainder and divisor
       subwf remdrH,w
       skpz 
       goto testgt   ; Not equal so test if remdrH is greater
       movfw divisL  ; High bytes are equal, compare low bytes
       subwf remdrL,w
testgt skpc          ; Carry set if remdr >= divis
       goto remrlt

subd   movfw divisL  ; Subtract divisor from partial remainder
       subwf remdrL
       skpc          ; Test for borrow

       decf remdrH   ; Subtract borrow
       movfw divisH
       subwf remdrH
       bsf divid0,0  ; Set quotient bit to 1
                     ; Quotient replaces dividend which is lost
remrlt decfsz bitcnt
       goto dvloop
       return

Comments:

• Thanks a lot , it workwed 4 pic16f628A. at least running in mplab sim.
  Cheer!+
• This routine worked great and saved me a ton of valuable time. Thank you very much. Brilliant.+
• It wouldn't hurt to change "movlw 32" to "movlw .32" (without quotes). If default radix isn't decimal, assembler will misinterpret that number...+

Questions:

• pic at harry-arends.nl asks: " How can i make this work on a 16F628A. I tryed this myself but wont work" James Newton replies: I don't see anything at first glance that should keep it from working on that chip. What error do you get when you try?+

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