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Newsgroups: comp.lang.ada
From: Ted Dennison<dennison@telepath.com>
References: <mailman.1010234881.12215.comp.lang.ada@ada.eu.org>
Subject: Re: A case where Ada defaults to unsafe?
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In article <mailman.1010234881.12215.comp.lang.ada@ada.eu.org>, Gautier
Write-only-address says...
>
>>If I use "and" and I'm wrong in assuming that the order doesn't matter,
>>then I have introduced a subtle bug. If I'm right, then I haven't gained
>>anything. So why not always use "and then"?
>
>The short circuit is not always the faster. A good compiler
>can much more aggressively optimize an "x>=0 and x<=xmax" than
>"x>=0 and then x<=xmax"; in addition "and then" introduces
>branch(es) in the machine code, this is a performance
>penalty on processors like the Pentiums.

Except that processors like the Pentiums also have branch prediction and
speculative execution. So it might not matter much after all. :-)

It gets really hairy doesn't it? That's why the best decision is to usually let
the compiler (and thus the CPU optimization experts) deal with it, rather than
trying to use the more restrictive option to hand-optimize the sources yourself.

---
T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html

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