Re: A86: Fw: Simple Division

To: assembly-86@lists.ticalc.org
Subject: Re: A86: Fw: Simple Division
From: rabidcow@juno.com (Joshua J Seagoe)
Date: Sat, 12 Dec 1998 08:35:25 -0800
Delivered-To: assembly-86-outgoing@towerguard.unix.edu.sollentuna.se
Reply-To: assembly-86@lists.ticalc.org


be patient

there's the divide-by-3 problem that just went by, in which there was
another that divided by anything but if you want to use 3 a lot then this
might be better.

use fixed point to multiply by .3333...
256*.333=$00.56=%00000000.01010110 (rounded up)

;de=number	use d=0,e=8-bit number if you want
;h=de/3
div3:
 ld h,d
 ld l,e
 add hl,hl	;*%00000010
 add hl,hl	;*%00000100
 add hl,de	;*%00000101
 add hl,hl	;*%00001010
 add hl,hl	;*%00010100
 add hl,de	;*%00010101
 add hl,hl	;*%00101010
 add hl,de	;*%00101011
 add hl,hl	;*%01010110
 ret

9*11+2*4=107 t-states, not including call/return

this will work up to $02fa, which gives 762/3=255.something instead of
254.whatever

ok, now divide by 6 is the same, without the last "add hl,hl"
107-11=96 t-states, not including call/ret
that should work twice as far as div3, up to $05f4

use them inline if you want to squeeze out every ounce of speed  (leave
out the ret then)

-josh

On Fri, 11 Dec 1998 21:05:29 -0600 "Dave M. Weprin"
<bioserr@megsinet.net> writes:
>
>Well since no one answered (very rude), here it is again...
>
>-----Original Message-----
>From: Dave M. Weprin <bioserr@megsinet.net>
>To: assembly-86@lists.ticalc.org <assembly-86@lists.ticalc.org>
>Date: Friday, December 11, 1998 5:00 PM
>Subject: A86: Simple Division
>
>
>>
>>All I need to know is the fastest way to divide an 8-bit integer by 3 
>and
>by
>>6.
>>
>>I know several ways of doing this, but I don't know of the fastest 
>way.
>Any
>>suggestions would be grately appreciated.  Remember, size doesn't 
>matter to
>>me very much, it's the speed that I'm most concerned about.
>>
>>Thanks
>>-Dave
>>
>
>

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