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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: and then... (a curiosity)
Date: Wed, 3 Sep 2008 07:14:11 -0700 (PDT)
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Date: 2008-09-03T07:14:11-07:00
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On Sep 2, 10:56 pm, Robert A Duff <bobd...@shell01.TheWorld.com>
wrote:
> Santiago Urue=F1a <suru...@gmail.com> writes:
> > suggest using plain "and" / "or" operators when just boolean flags are
> > involved because it is usually faster to evaluate all the variables
> > than using lazy evaluation.
>
> I don't buy that argument, because the semantics of "A and B and C"
> are identical to the semantics of "A and then B and then C" (when A, B,
> and C are Boolean variables),

*Almost* true.  It isn't true when some of those Boolean variables
have 'Address clauses that cause them to be mapped to hardware I/O
registers!!  But I know what you meant.  I'd go so far as to say a
good compiler should generate the exact same code when the arguments
are (normal, non-volatile) Boolean variables whether or not you use
"and" or "and then", and similarly "or" or "or else".  It should just
pick whatever is fastest.

                                -- Adam