Date: Tue, 28 Nov 1995 23:37:00 +0100 (MEZ) From: wolf@prz.tu-berlin.de To: mrami@minerva.cis.yale.edu Cc: sysseh@devetir.qld.gov.au, chat@freebsd.org Subject: Re: Anybody with a Turbo C++ compiler able to answer a couple of questions? Message-ID: <199511282237.XAA26907@tubkom.prz.tu-berlin.de> In-Reply-To: <Pine.BSF.3.91.951128003600.2639E-100000@mramirez.sy.yale.edu> from "Marc Ramirez" at Nov 28, 95 00:43:00 am
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Marc Ramirez wrote:
>
> On Tue, 28 Nov 1995, Stephen Hocking wrote:
>
> > What do the macros FP_SEG & FP_OFF do? I think that they are for getting the
> > segment number & offset respectively of a pointer, but am not sure.
>
> I believe you're right. Grep (TC comes with grep! I love that!) through
> dos.h. If I remember correctly, it's in there (god, I haven't used Turbo
> C since I was 15 or so). It should, of course, say something like
>
> #define FP_SEG(x) ((long)(x)<<16L)
> #define FP_OFF(x) ((long)(x)&65535L)
>
At least in Borland C++ the definition is actually:
#define FP_SEG( fp ) ( (unsigned) (void _seg *)(void far *)( fp ))
#define FP_OFF( fp ) ( (unsigned) ( fp ))
This is because a "far" pointer ("far" means more then 64k) is
32 bits long but not stored as any normal human expects, but instead
with a 16 bit offset in the first two bytes and a 16 bit segment
in the second two bytes, as in the 8086/8088 days (at least in
the classical "memory models").
Thomas
--
Thomas Wolfram <thomas@aeon.in-berlin.de> Germany: 0 30 31421171
PRZ TU Berlin <wolf@prz.tu-berlin.de> abroad: +49 30 31421171
EANTC WWW: http://www.prz.tu-berlin.de/~wolf
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