Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uunet!cs.utexas.edu!asuvax!ncar!tank!phd_ivo@gsbacd.uchicago.edu
From: phd_ivo@gsbacd.uchicago.edu
Newsgroups: gnu.gcc
Subject: Re: IEEE FLP question: Use of NAN and Inf
Message-ID: <6835@tank.uchicago.edu>
Date: 21 Dec 89 18:24:25 GMT
Sender: news@tank.uchicago.edu
Organization: University of Chicago Graduate School of Business
Lines: 25

> 
>	Try 
>		float f;
>		*(int*)&f = 0x80000000;
> 
>	this works on every c compiler I'm aware of.

Yes, with floats, but not with doubles. Moreover, since it's not a
preprocessor definition, its ugly when your code should read

	f=NaN;

at some spot. The best ways to deal with these IEEE numbers (thanks for all
the mail) are probably:

	#define NaN (0.0/0.0)
	#define Inf (1.0/0.0)
	#define isNaN (x!=x)

One problem here is that I would like to generate a signal (exception/interupt)
when an invalid operation is attempted. However, if this is possible on some
computer(s), then the above definition will generate this upon assignment---
which is clearly not the intended result.

/ivo