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From: kers@hplb.hpl.hp.com (Chris Dollin)
Newsgroups: comp.lang.c
Subject: Re: The nonexistent operator (along = v. == lines)
Message-ID: <KERS.91Apr5151131@cdollin.hpl.hp.com>
Date: 5 Apr 91 14:11:31 GMT
References: <156@revcan.UUCP> <157@revcan.UUCP> <1991Apr3.203748.3226@neon.Stanford.EDU>
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In-Reply-To: dkeisen@Gang-of-Four.Stanford.EDU's message of 3 Apr 91 20:37:48 GMT
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Dave Eisen writes (apropos of the ``xor'' discussion):

   #define XOR(a,b)	(!!(a) ^ !!(b))
   does what you want.

Hmm ... we can strip one of the !'s from each pair to get

    (!(a) ^ !(b))

If the XOR is likely to be used in conditional contexts (rather than value
contexts) then I'd guess that more compilers could optimise equality tests than
^ instructions (because more machines have some sort of branch-if-(n)eq), so
how about

#define XOR(a,b)   (!(a) != !(b))


--

Regards, Kers.      | "You're better off  not dreaming of  the things to come;
Caravan:            | Dreams  are always ending  far too soon."