Message-Id: <200003221719.MAA17164@delorie.com>
From: "Dieter Buerssner" <buers AT gmx DOT de>
To: djgpp-workers AT delorie DOT com
Date: Wed, 22 Mar 2000 18:19:40 +0100
MIME-Version: 1.0
Content-type: text/plain; charset=US-ASCII
Content-transfer-encoding: 7BIT
Subject: Re: Unnormals???
CC: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
References: <200003221407 DOT JAA07300 AT delorie DOT com>
In-reply-to: <Pine.LNX.4.10.10003221526130.29657-100000@acp3bf>
X-mailer: Pegasus Mail for Win32 (v3.12b)
Reply-To: djgpp-workers AT delorie DOT com

On 22 Mar 00, at 15:44, Hans-Bernhard Broeker wrote:

[I added four zeroes in the next two lines]

> > >  pos_nanshort = 7fff 0001 0000 0000 0000
> > >  neg_nanshort = ffff 0001 0000 0000 0000
[...]
> So they are 'Pseudo-NaN', in the sense that they look a bit like NaN,
> but aren't, as they do not have the leading '1' bit in the mantissa
> required for NaNs, or any number that is not an unnormal.

I admit, that I have chosen the example numbers very unluckily. I 
just wanted to show, that you can use the casting method to load
such numbers into an FPU register. I apologize for giving wrong 
information.

That I thought, that these numbers are "normal" NaNs comes from the
reading of a paper by David Goldberg (What every Computer Scientist 
should know about Floating-Point Aritmetic).  In this paper he 
defines a IEEE NaN as any number with an exponent of emax+1 and any 
non-zero mantissa. I think David Goldberg was working on the IEEE 
standards, so I trusted this definition.

Anyway, to be in conformance with C99 for printf, and to be 
consistant with copysign and signbit, I think for NaNs (quiet and 
signalling) and also for pseudo NaNs, printf should print [-]NAN.
For unnormals, it could print [-]NAN(unnormal) or [-]NAN.

BTW. Does anybody understand, what pseudo Infinities are?
(Described in the Intel manual under 7.4.4)

Regards, 
Dieter