OpenEuphoria

Re: modified reverse

• Posted by rforno at tutopia.com Aug 07, 2001
• 534 views

Rob, I do not understand. floor(anything) should always be an integer. It
seems that x being an integer does not matter.
----- Original Message -----
From: "Robert Craig" <rds at RapidEuphoria.com>
To: "EUforum" <EUforum at topica.com>
Subject: Re: modified reverse


>
> Derek Parnell writes:
> > Strange but I found rforno's version slightly slower (96%) than the
> > standard.
>
> Yes, I searched the mailing list archives, and found a comparison
> I did between the current reverse() and a version identical to
> rforno's 3 years ago. I was using my old Pentium-150 machine,
> and found the current reverse() was faster. That's why I chose it.
> Now I have a Pentium II with a different cache size etc.
>
> > One way to get the standard one going slightly faster is to force
> > an integer conversion of the floor() function.
> > Because the floor() function is in the for..loop, Euphoria assumes
> > that it is possible to generate a really big result and does
> > tests for atom-ness and integer overflow on every
> > comparison of the 'upper' variable. It even does extra
> > work when adding one to it for the next iteration,
> > just in case it overflows the integer bounds.
>
> Good idea. I'll assign to an integer before the loop.
>
> Note that this helps the translated code quite a bit,
> but helps the interpreter very little because the interpreter
> decides each time at the start of a for-loop (after
> evaluating the expressions) whether
> the loop variable can only have integer values or not
> during the loop. It then self-modifies some of
> the code for the loop. The translator has to decide once
> and for all at compile-time when it generates the C code.
> If there is any doubt (as in this case), it can't assume integer-only.
> The only alternative for the translator would be to
> to generate multiple copies of the entire loop and choose
> one of them at the start, at run-time.
> This would typically be a lot of C code to generate.
>
> (Of course if the translator were *really* smart, it would realize that
> floor(x/2)+1 must always be an integer, if x is an integer).
>
> Regards,
>    Rob Craig
>    Rapid Deployment Software
>    http://www.RapidEuphoria.com
>
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