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From: guertinp@IRO.UMontreal.CA (Paul Guertin)
Subject: Re: ASM multiply/divide
Message-ID: <CsLAED.M63@IRO.UMontreal.CA>
Sender: news@IRO.UMontreal.CA
Organization: Universite de Montreal, Canada
References: <2veuv9$1u6@atlas.cs.upei.ca> <2vgkqu$g64@atlas.cs.upei.ca>
Date: Thu, 7 Jul 1994 21:30:12 GMT
Lines: 28

Here's a 16-by-8 bit unsigned divide that I used in a program to
calculate many decimals of pi.
 
Input in dvend, dvend+1 (lsbyte first) and dvsor.
Output in dvend (quotient) and dvend+1 (remainder).
 
Of course, since the quotient is 8 bits wide, you must ensure that
floor(dividend/divisor) < 256.
 
I didn't count cycles, but it should take around 200 cycles average.
 
     ldx #9
     lda dvend+1
loop rol dvend
     dex
     beq end
     rol
     bcs foo
     cmp dvsor
     bcc loop
foo  sbc dvsor
     sec
     bcs loop
end  sta dvend+1
     rts
 
Paul Guertin
guertinp@iro.umontreal.ca