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From: ark@alice.UucP (Andrew Koenig)
Newsgroups: net.lang.c
Subject: Re: /-INFINITY and NaN
Message-ID: <4745@alice.UUCP>
Date: Wed, 25-Dec-85 10:04:58 EST
Article-I.D.: alice.4745
Posted: Wed Dec 25 10:04:58 1985
Date-Received: Thu, 26-Dec-85 03:56:33 EST
References: <978@brl-tgr.ARPA>
Organization: Bell Labs, Murray Hill
Lines: 21

> A question was raised as to how to compare a float (or double) to
> the ANSI +/-infinity and Not-a-Number values.  One suggestion was to
> use a struct; another way (though arguably not elegant) is-
>	#define INFINITY	(*(float*)"\177\200\0\0")
>	#define NaN		(*(float*)"\177\277\377\377")
> (I'm not certain of the bit patterns, however). The idea is to cast a
> string, which is coerced into a char*, into a float*, thus interpreting
> the string chars as elements of a float data value.
> The same idea can be extended to doubles.
> (This works on one compiler that I know of, running on an 8086).
>
>While this may not seem elegant, it has the advantage of not requiring
>any structure initilizations.
>
>	David R. Tribble	<tribble_acn@uta>

It has the disadvantage of being extremely implementation-specific.

In general, there may be variation from one implementation to another
as to the location of the various bits within a word.  There may also
be alignment problems with this technique on some machines.