Date: Thu, 19 Dec 1996 09:03:29 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To: "John M. Aldrich" <fighteer AT cs DOT com>
cc: shaman AT nlc DOT net DOT au, djgpp AT delorie DOT com
Subject: Re: windows <-> cwsdpmi
In-Reply-To: <32B8B3EE.7AEC@cs.com>
Message-ID: <Pine.SUN.3.91.961219085709.24763N-100000@is>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII


On Wed, 18 Dec 1996, John M. Aldrich wrote:

> The malloc() used by DJGPP rounds the size of allocated memory blocks to
> the next higher power of 2.  So, allocating 300 bytes gets you 512;
> allocating 1500 bytes gets you 2048, and allocating 8 MB + 1 gives you
> 16 MB.

Actually, even "malloc (8 * 1024 * 1024)" will ask for 16MB, because 
`malloc' needs a few more bytes for its overhead for every allocation 
(how else would it know the size of the buffer when you `free' it?).  So 
you should ask for a bit less than 8MB to get 8MB.

>  This, unfortunately, is a speed optimization of the GNU C
> compiler, so it can't easily be changed.

It has nothing to do with the compiler.  It's just a (mis)feature of the 
`malloc' algorithm in DJGPP library (taken from the BSD libc, if memory 
serves).  Volunteers are welcome to suggest alternative implementations 
of `malloc' & Co., which are free of this problem.

> or set DPMI memory to 64 MB in the Control Panel (win95).

On Windows 95, this is done in the property sheet of the DOS box, not in 
the Control Panel.