Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!snorkelwacker!spdcc!ima!haddock!karl
From: karl@haddock.ima.isc.com (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: IsUnsigned() function?
Message-ID: <17115@haddock.ima.isc.com>
Date: 18 Jul 90 20:16:14 GMT
References: <1990Jul16.214155.5087@Neon.Stanford.EDU>
Reply-To: karl@kelp.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Cambridge, MA 02138-5302
Lines: 13

In article <1990Jul16.214155.5087@Neon.Stanford.EDU> jhsu@Neon.Stanford.EDU (Jeffrey H. Hsu) writes:
>How would you write a space efficient algorithm/function in C that
>takes in an integer and returns 0 if signed and 1 if unsigned?

Define your terms.  Is this to be a function or a macro?  If a function, then
its argument must have a type known at compile-time: what type is it?  Is the
goal to determine the signedness of the type of the argument, or the value?

A non-trivial specification is to write a macro to find the signedness of the
(promoted) type of its argument expression.  One way to do this is
	#define IsUnsigned(x) (((x)*0-2)/2+1 != 0)

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