[26061] in Perl-Users-Digest
Perl-Users Digest, Issue: 8267 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Thu Jul 21 21:05:28 2005
Date: Thu, 21 Jul 2005 18:05:03 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Thu, 21 Jul 2005 Volume: 10 Number: 8267
Today's topics:
Re: Strange speed-increase by separating "if"s <No_4@dsl.pipex.com>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Thu, 21 Jul 2005 23:22:34 +0100
From: Big and Blue <No_4@dsl.pipex.com>
Subject: Re: Strange speed-increase by separating "if"s
Message-Id: <KrSdneDW2u6xvX3fRVnyjQ@pipex.net>
Wolfram Humann wrote:
t...
> If my brain isn't totally drained already the correctly split version
> should be:
>
> if ($_ =~ /$c_dot[$d]/)
> {
> if ($1 < $x - $r - 2 or
> $1 > $x + $r + 2 or
> $2 < $y - $r - 2 or
> $2 > $y + $r + 2)
> {
>
> Naturally, with this the timing is more or less back to what it was.
> According to profiling, the four comparisons take about as much time as
> the pattern match -- hence the speed increase when they never executed :-)
You are (probably) doing 4 calculations to work out constants.
Might be quicker if you did:
$x_less_r2 = $x - $r - 2;
$x_plus_r2 = $x + $r + 2;
$y_less_r2 = $y - $r - 2;
$y_plus_r2 = $y + $r + 2;
(having declared them in a suitable scope) as soon as you get x and y then
change your test to use the calculated version. Of course, it depends on
how many times the test is run for each head branch taken (and whether Perl
optimizes this anyway).
--
Just because I've written it doesn't mean that
either you or I have to believe it.
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
From: Perl-Users-Request@ruby.oce.orst.edu (Perl-Users-Digest Admin)
Subject: Digest Administrivia (Last modified: 6 Apr 01)
Message-Id: <null>
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End of Perl-Users Digest V10 Issue 8267
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