From:	Luke Anthony Hutchinson <lhutchin AT ug DOT cs DOT su DOT oz DOT au>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Another way to access VGA memory
Date:	Mon, 28 Oct 1996 16:51:37 +1100
Organization:	Basser Dept of Computer Science, University of Sydney, Australia
Lines:	17
Message-ID:	<327449E9.7BAFE65D@ug.cs.su.oz.au>
References:	<961023180905_339586309 AT emout17 DOT mail DOT aol DOT com> <54n92c$hbr AT troll DOT powertech DOT no>
NNTP-Posting-Host:	congo.ug.cs.su.oz.au
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

> >Using near pointers in no quicker because you still have to
> >load the %edi register with your pointer and then no doubt add some stuff to
> >this to access the right pixel. With my method you load %es or whatever and
> >then load stuff into %edi to point to the right pixel  - so it is not slower
> >(apart from perhaps another register to save on the stack, although a push
> >and a pop will hardly slow a program down even if done hundreds of times a
> >second).
> 

Firstly, near pointers are quicker, as segment loads are slooow in prot.
mode.  Secondly I reckon using __djgpp_nearptr_enable(), is the most
elegant solution, infact most dos extenders have the data descriptor
limit set to 0FFFFFFFFh as the default (eg:DOS4G/W).  Infact, descriptor
limits <0FFFFFFFFh are such a pain in the arse that I extend the code
descriptor limits as well (for VBE prot. mode interface etc).

Luke

- Raw text -