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From: fritz AT dibe DOT unige DOT it (Fabrizio Giudici)
Newsgroups: rec.games.programmer,comp.os.msdos.djgpp,comp.os.msdos.programmer,comp.graphics.algorithms
Subject: Re: Fixed-point Math Library
Followup-To: rec.games.programmer,comp.os.msdos.djgpp,comp.os.msdos.programmer,comp.graphics.algorithms
Date: 2 Oct 1995 11:22:42 GMT
Organization: University of Genoa
Lines: 30
References: <43rf7k$cdj AT freenet3 DOT scri DOT fsu DOT edu> <44edp8$3vc AT due DOT unit DOT no>
Nntp-Posting-Host: poseidon.dibe.unige.it
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Dj-Gateway: from newsgroup comp.os.msdos.djgpp

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!!

Good luck...

--
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| Fabrizio Giudici, PhD Student (fritz AT dibe DOT unige DOT it) |                     |
|   WWW-PAGE: http://poseidon.dibe.unige.it/~fritz/   | Style distinguishes |
|          PHONE: +39 10  3532163 / 3532780           |   excellence from   |
|      Dept. of Biophys. and Elect. Eng. (DIBE)       |   accomplishment.   |
|     University of Genoa - ITALY, EUROPE, EARTH      |                     |
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 All expressed opinions are personal and not of the organization I work for.