Re: Re: file name parsing to get the original file name


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Re: Re: file name parsing to get the original file name

by MarkM (Curate)

on Aug 20, 2003 at 20:30 UTC ( [id://285288]=note: print w/replies, xml )

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in thread file name parsing to get the original file name

Interesting. It looks like you've found yet another piece of Perl that isn't implemented in the most optimal manner. :-)

Playing around, I found that on my system, the following tweak allows the 'single regexp match' to beat the 'split into a temporary list, and grab the last entry' approach by ~15%:

$f =~ /(?:.*\/)?(.+)/s; my $fn = $1;

I'm still surprised that Perl can match against '/' several times (split) faster than it can skip to the last '/' with a single rather simple match. It seems the Perl regular expression engine could still use a few optimizations. Until then, I suppose explicit optimization isn't that bad.

Cheers,
mark

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Re: file name parsing to get the original file name
by Abigail-II (Bishop) on Aug 20, 2003 at 21:22 UTC

I'm still surprised that Perl can match against '/' several times (split) faster than it can skip to the last '/' with a single rather simple match.

I'm not surprised. /(^\/+)\z/ is a rather complicated regex due to the character class being used. The optimizer can't figure out that is the same as "looking for the last slash". m!/! on the other hand is so simple, the optimizer recognizes it as searching for a fixed string.

Abigail

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