[A83] Re: HL = A * 12 (fast)

To: assembly-83@lists.ticalc.org
Subject: [A83] Re: HL = A * 12 (fast)
From: Harper Maddox <gte172i@prism.gatech.edu>
Date: Tue, 23 Apr 2002 09:34:51 -0400
In-Reply-To: <009a01c1eac8$beec4ac0$d905040a@tijl>
References: <3CC6443C.950976B8@dingoblue.net.au>
Reply-To: assembly-83@lists.ticalc.org


This is such a simple algorithm, i've probably written it a hundred 
times.  If you guys want a challenge, how about you write a divide hl by 12 
algorithm.  I use that a lot for collision detection with my projects that 
use 12x12 pixel tiles.

harper

At 03:13 PM 4/23/02 +0200, you wrote:

>I got ye beaten ;P Who does better?
>
>
>ld     l,a
>add    a,a     ; *2
>add    a,l     ; *3
>ld     l,a
>ld     h,0
>add    hl,hl   ; *6
>add    hl,hl   ; *12
>
>
>
>----- Original Message -----
>From: "Darren" <qarnos@dingoblue.net.au>
>To: <assembly-83@lists.ticalc.org>
>Sent: Wednesday, April 24, 2002 7:35 AM
>Subject: [A83] HL = A * 12 (fast)
>
>
> >
> >
> > I wrote this little piece of code to calculate HL = A * 12. It seems to
> > be a bit faster than anything else I could find, so maybe some of you
> > could benefit from it, or prove me wrong! :)
> >
> > It takes 46 T-states, and destroys A:
> >
> >     add    a, a    ; A * 2
> >     ld    l, a
> >     add    a, a    ; A * 4
> >     add    a, l    ; A * 6
> >     ld    l, a
> >     sbc    a, a
> >     and    1
> >     ld    h, a
> >     add    hl, hl    ; A * 12
> >
> >
> >
> >
> >

Follow-Ups:

[A83] Re: HL / 12 (fast)

From: "Tijl Coosemans" <tijl@ulyssis.org>

References:

[A83] HL = A * 12 (fast)

From: Darren <qarnos@dingoblue.net.au>

[A83] Re: HL = A * 12 (fast)

From: "Tijl Coosemans" <tijl@ulyssis.org>