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From:	kptben AT aol DOT com (KPT Ben)
Newsgroups:	rec.games.programmer,comp.os.msdos.djgpp,comp.os.msdos.programmer,comp.graphics.algorithms
Subject:	Re: Fixed-point Math Library
Date:	2 Oct 1995 08:18:42 -0400
Organization:	America Online, Inc. (1-800-827-6364)
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References:	<44oi23$1gt AT alpha DOT cisi DOT unige DOT it>
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To:	djgpp AT sun DOT soe DOT clarkson DOT edu
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fritz AT dibe DOT unige DOT it (Fabrizio Giudici) wrote:

>In article <43rf7k$cdj AT freenet3 DOT scri DOT fsu DOT edu>, joeo AT freenet2 DOT scri DOT fsu DOT edu
>says...
>>
>>I'm trying to write some very simple 3d stuff for a DOS machine using 
>>DJGPP, but the floating point stuff is just WAYYYY too slow on my
machine 
>>(a 486SX). So I tried using integral math (multiplying all results by 
>>10000 or more), but that causes all results to eventually end up at zero

>>due to rounding and precision losses.
>
>A suggestion: don't multiply for a ten power, but use a two power!! For 
>example, use 10240 instead of 10000, so you'll able to change many
rescaling 
>mul/divs into simpler (and faster) bit-shifts!!
>
>Concerning precision losses, try to use just a few bits (i.e. multiply
for
>256 or 512 instead of 10240), or however make experiments with many
values:
>often too many decimal bits are a waste and more decimal bits ==> more
chances
>of overflow. For example, I'm writing a complex (and working ;-) 3-D
engine
>for a flight simulator for which 8-bits (x 256) are pretty good!!

Uh, 10240 is not a power of 2, last time I checked... try 8192 or 16384 :)

--
Ben Weiss
Senior Software Engineer
MetaTools Inc. (formerly HSC Software)

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