From: Kovacs Viktor Peter <vps AT winnie DOT obuda DOT kando DOT hu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: MISSION: Making world´s fastest pixel drawing possible
Date: Thu, 18 Jan 2001 12:34:35 +0000
Organization: Budapest University of Technology and Economics
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> Contents:
> - Fastest possible way to draw pixel´s (well, maybe the near pointer hack
> mentioned in DJGPP FAQ is faster :)). Drawing developed as a macro (becourse
> jumping to function and back again takes more time than drawing the damn
> pixel !). Screen coordinates pre-calculated in the global table.
> 
> Feedback needed about the following subjects:
> 1) Is it necessary to save ES segment register (the macro currently does not
> do it, but it seems to work fine, no crashes, etc...) ?
> 2) Is the assembly command "les    %0,%%edi" faster than the currently used
>  "movw    %0,%%es;movl %1,%%edi" pair ?

 Have you heard about the far ptr hack in djgpp? It even allows loading
 the segment outside a tight loop...
 (It was designed to work with systems that don't allow segment limits
 to be set to 4GB.)
 
 About your questions:
  -yes, you should save ES, because someone (memcpy) might use it...
  -les: On the P4 it is slower, on other systems it is about the same
  -precalculated tables: when you use integer math only, it is faster to
   calculate it on the fly, because you can spare a few TLB and cache
   entries with it (the overall speed will be faster)
  -tables are to be used instead of float math...