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From: ark@alice.UUCP (Andrew Koenig)
Newsgroups: comp.lang.c
Subject: Re: Floating point exceptions
Keywords: NAN, Infinity
Message-ID: <11142@alice.UUCP>
Date: 4 Aug 90 14:18:29 GMT
References: <446@demott.COM>
Organization: AT&T Bell Laboratories, Liberty Corner NJ
Lines: 17

In article <446@demott.COM>, kdq@demott.COM (Kevin D. Quitt) writes:

>     I need to be able to examine an IEEE double to see if it is anything
> but a number (e.g. NAN) *before* I actually try to use it.

If your implementation is nice to you, you will have some library
function like isNaN().

If not, then you're supposed to be able to turn traps off and
(I think) check whether the number is equal to itself (!) --
I believe that all six relational operators are supposed to
return `false' if either operand is a NaN.  If you have a
signalling NaN, though, you'd better make sure you turn traps
off.
-- 
				--Andrew Koenig
				  ark@europa.att.com