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From: karl@haddock.ima.isc.com (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: IsUnsigned() function?
Message-ID: <17147@haddock.ima.isc.com>
Date: 25 Jul 90 00:44:37 GMT
References: <1990Jul16.214155.5087@Neon.Stanford.EDU> <2936@mtung.ATT.COM> <1990Jul22.154326.19680@ux1.cso.uiuc.edu> <615@tetrauk>
Reply-To: karl@kelp.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Cambridge, MA 02138-5302
Lines: 19

In article <615@tetrauk> rick@tetrauk.UUCP (Rick Jones) writes:
>I'm suprised that very few people seems to have grasped what the question was
>about.

It's because the question was so poorly worded (as posted; I don't know if it
was asked the same way).  Maybe that was the intent: to see if the interviewee
would give the correct response, "What do you mean?", rather than immediately
starting to write code.

>#define IsUnsigned(a)	(a >= 0 && ~a >= 0)

I think my version is more likely to fold into a compile-time constant.  (I
used `((a)*0-2)/2+1 != 0', which is intended to be fairly robust even against
questionable compilers.)  And why assume 2's-complement if you don't have to?

Trivia question: under what circumstances will Rick's macro produce the wrong
answer to the presumed question?

Karl W. Z. Heuer (karl@kelp.ima.isc.com or ima!kelp!karl), The Walking Lint