Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!tdatirv!sarima
From: sarima@tdatirv.UUCP (Stanley Friesen)
Newsgroups: comp.lang.c
Subject: Re: NaN's (was Re: FLOATING NULL?)
Message-ID: <14@tdatirv.UUCP>
Date: 31 May 91 19:23:13 GMT
References: <13223@uhccux.uhcc.Hawaii.Edu> <1991May28.153655.24199@zoo.toronto.edu> <2726@root44.co.uk>
Reply-To: sarima@tdatirv.UUCP (Stanley Friesen)
Organization: Teradata Corp., Irvine
Lines: 14

In article <2726@root44.co.uk> gwc@root.co.uk (Geoff Clare) writes:
>I agree there is no standard way of generating NaN (although sqrt(-1.0)
>is your best bet).  However, there is a standard way of testing for NaN.
>If x is a floating point variable, then (x != x) will be TRUE if and
>only if x has the value NaN.

But what if the compiler notices you are asking for a self comparison and
optimizes it away?  Then this will fail unless x is volatile.

Since NaN's fall in the area of unspecified/undefined behavior I believe
that such an optimization is legal under the ANSI standard.
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uunet!tdatirv!sarima				(Stanley Friesen)