Groups > comp.sys.apple2.programmer > #385

Re: FAST 6502 DIVIDE BY 14?

From	aiiadict@gmail.com
Newsgroups	comp.sys.apple2.programmer
Subject	Re: FAST 6502 DIVIDE BY 14?
Date	2012-08-14 13:53 -0700
Organization	http://groups.google.com
Message-ID	<da655564-da59-4eb0-bc15-a6f0b30e9af8@googlegroups.com> (permalink)
References	<4510fd05-bef3-433a-8f6d-764da886f214@googlegroups.com> <8c74c952-aa50-4257-85cd-3491d8ee923e@googlegroups.com> <k0ed1u$mif$1@news.xmission.com> <k0eddt$n0f$1@news.xmission.com>

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On Tuesday, August 14, 2012 1:45:47 PM UTC-7, datajerk wrote:
> On 8/14/12 2:39 PM, Egan Ford wrote:
> 
> > On 8/14/12 2:21 PM, BLuRry wrote:
> 
> >> Consider divide by 14 as a divide by 2 (easy!) and then by 7.
> 
> >>
> 
> >> Divide by 7:
> 
> >> DIVIDE_BY_SEVEN:
> 
> >>    LDA BYTE
> 
> >>    LSR
> 
> >>    LSR
> 
> >>    LSR
> 
> >>    ADC BYTE
> 
> >>    ROR
> 
> >>    LSR
> 
> >>    LSR
> 
> >>    ADC BYTE
> 
> >>    ROR
> 
> >>    LSR
> 
> >>    LSR
> 
> >>    RTS
> 
> >>
> 
> >> On Tuesday, August 14, 2012 3:09:29 PM UTC-5, (unknown) wrote:
> 
> >>> i'VE seen tricks for doing different divides
> 
> >>>
> 
> >>> using 6502...
> 
> >>>
> 
> >>>
> 
> >>>
> 
> >>> are there any for divide by 14?
> 
> >>>
> 
> >>>
> 
> >>>
> 
> >>> input = 1 byte
> 
> >>>
> 
> >>> output = byte / 14, remainder
> 
> >>>
> 
> >>>
> 
> >>>
> 
> >>>
> 
> >>>
> 
> >>> Rich
> 
> >>
> 
> >
> 
> > BLuRry beat me to it:
> 
> >
> 
> >          lda     #$5F        ; load dividend in a
> 
> >          jsr     div14        ; /14 it
> 
> >          sta     result        ; result is in a
> 
> >          rts
> 
> >
> 
> > div14:
> 
> >          sta     dividend
> 
> >          lsr
> 
> >          lsr
> 
> >          lsr
> 
> >          adc     dividend
> 
> >          ror
> 
> >          lsr
> 
> >          lsr
> 
> >          adc     dividend
> 
> >          ror
> 
> >          lsr
> 
> >          lsr                     ;div by 7
> 
> >          lsr                     ;div by 2 (14)
> 
> >          rts
> 
> >
> 
> >
> 
> 
> 
> Here is a better one that give you /7 and /14.
> 
> 
> 
> div14:
> 
>          lsr
> 
> div7:
> 
>          sta     dividend
> 
>          lsr
> 
>          lsr
> 
>          lsr
> 
>          adc     dividend
> 
>          ror
> 
>          lsr
> 
>          lsr
> 
>          adc     dividend
> 
>          ror
> 
>          lsr
> 
>          lsr
> 
>          rts
> 
> 
> 
> Remainder is missing.  Is that required?

yUP...

How do you get from divide by 7, or divide by 14, to the above code?  I've seen descriptions of how to do it in 6502 assembly language textbooks, but I've never understood it.

Rich

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Thread

FAST 6502 DIVIDE BY 14? aiiadict@gmail.com - 2012-08-14 13:09 -0700
  Re: FAST 6502 DIVIDE BY 14? aiiadict@gmail.com - 2012-08-14 13:14 -0700
  Re: FAST 6502 DIVIDE BY 14? BLuRry <brendan.robert@gmail.com> - 2012-08-14 13:21 -0700
    Re: FAST 6502 DIVIDE BY 14? BLuRry <brendan.robert@gmail.com> - 2012-08-14 13:24 -0700
    Re: FAST 6502 DIVIDE BY 14? Egan Ford <datajerk@gmail.com> - 2012-08-14 14:39 -0600
      Re: FAST 6502 DIVIDE BY 14? Egan Ford <datajerk@gmail.com> - 2012-08-14 14:45 -0600
        Re: FAST 6502 DIVIDE BY 14? aiiadict@gmail.com - 2012-08-14 13:53 -0700
          Re: FAST 6502 DIVIDE BY 14? Egan Ford <datajerk@gmail.com> - 2012-08-14 14:59 -0600
          Re: FAST 6502 DIVIDE BY 14? Egan Ford <datajerk@gmail.com> - 2012-08-14 15:08 -0600
        Re: FAST 6502 DIVIDE BY 14? Egan Ford <datajerk@gmail.com> - 2012-08-14 14:54 -0600
  Re: FAST 6502 DIVIDE BY 14? Antoine Vignau <antoine.vignau@laposte.net> - 2012-08-14 15:38 -0700
    Re: FAST 6502 DIVIDE BY 14? aiiadict@gmail.com - 2012-08-16 21:25 -0700
  Re: FAST 6502 DIVIDE BY 14? Michael J. Mahon <mjmahon@aol.com> - 2012-08-14 19:14 -0500

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