32-BIT DIVISION - Oct 02 issue

I recently asked Peter Hemsley how easy it would be to expand his PIC
16-bit/16-bit division routine (in the PIC Tricks folder on our ftp) to
32-bit/16-bit. He replied:

If there is a Carry out from the Shift left then force the subtraction, as
in the following. This has not been thoroughly tested but seems to work OK.
By the way, a 32/32 divide would involve a 32-bit comparison and a 32-bit
subtraction. A tiresome job in PIC language.

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

Peter Hemsley, via email

That's brilliant Peter! - I'll add it to PIC Tricks. Thank you from me and
all PIC Trickers!

10Oct'02
**** this line was incorrect in published issue. The code now works excellently - well done Peter.