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From: george@hls0.hls.oz (George Turczynski)
Newsgroups: comp.lang.c
Subject: Re: TRUE and FALSE
Message-ID: <931@hls0.hls.oz>
Date: 11 Sep 90 01:16:49 GMT
References: <11215@alice.UUCP> <514@demott.COM> <2316@cirrusl.UUCP> <728@tetrauk.UUCP>
Lines: 54

In article <728@tetrauk.UUCP>, simons@tetrauk.UUCP (Simon Shaw) writes:
> In article <926@hls0.hls.oz> george@hls0.hls.oz (George Turczynski) writes:
> >Why not try these:
> > 
> >#define CNOT(a)        (!(a)) 
> >#define CAND(a,b)      ((a)&&(b)) 
> >#define COR(a,b)       ((a)||(b)) 
> >#define CNOR(a,b)      CNOT(COR(a,b)) 
> >#define CXOR(a,b)      CNOR(CAND(a,b),CNOR(a,b)) 
> 
> If because the value returned by an expression of the form (a == b)
> is _defined_ to be 0 or 1, we are defining TRUE as 1 and ZERO as 0
> (no contention yet, I hope), then the worst of these expansions, 
> XOR, should be contracted by the use of the bitwise XOR.
> 
> #define	CXOR(a,b) ((a)^(b))

No, I think not.  These macros all return a result that is TRUE or FALSE.
The bitwise XOR operator will not always produce the result TRUE or FALSE.
These macros are not performing bitwise arithmetic, but logical arithmetic.

> with this assumption (TRUE==1, FALSE==0), are there any circumstances 
> where the use of the bitwise operator would be unsafe ?

In this case, yes.  If someone were to say:-

	if( CXOR(a,b) == TRUE )

they would in most cases be in trouble, if the XOR operator was used.  Now,
you and I both know that few people would construct it like that, but that
is beside the point, these macros ALWAYS result in TRUE or FALSE.

> IMHO, the compounds NOR and NAND, while much more useful if constructing 
> electronic circuitry, are considerably less clear in code (Not to mention
> XNOR, which even now takes me a few seconds to work out).  Lets not
> forget the poor sods who've got to maintain this code !
> 
> Anyone disagree ?

Don't think for one second that I would entertain the idea of using these macros !
Felix Lee posted his set, some of which expanded to 200,000++ characters.
Thinking this was ridiculous, and that I might save some people wasting too
much of their time, I posted the same (but improved) macro set, that didn't
waste so much space.

I agree, don't waste your time with the above macros.  (But Felix Lee could
at least use the sensible ones, not the 200,000++ char ones :-})

-- 
| George P. J. Turczynski.          |---------------------------------------------------- 
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