Re: RegEx Perl Code

I'm not convinced that so called "compiled regular expressions" are significantly faster. Here's a benchmark, matching IP addresses. One using the 'variable' approach, and one using compiled regular expressions:

#!/usr/bin/perl

use strict;
use warnings 'all';
 
use Benchmark;
 
use vars qw /$ip_v $ip_re @data/;

my $quad_v   = q  '(?:25[0-5]|2[0-4]\d|1\d\d|\d\d?)';
my $quad_re  = qr '(?:25[0-5]|2[0-4]\d|1\d\d|\d\d?)';
 
my $sep_v    = q  '\.';
my $sep_re   = qr '\.';
 
   $ip_v     = qq "$quad_v$sep_v$quad_v$sep_v$quad_v$sep_v$quad_v";   
+          
   $ip_re    = qr "$quad_re$sep_re$quad_re$sep_re$quad_re$sep_re$quad_
+re";
 
   @data = map {join "." => map {int rand 1000} 1 .. 4} 1 .. 1_000; 
 
timethese -5 => {
    var  =>  'for (@data) {/$ip_v/}',
    re   =>  'for (@data) {/$ip_re/}',
};
__END__
[download]

Running this results in:

Benchmark: running re, var for at least 5 CPU seconds...
        re:  5 wallclock secs ( 5.25 usr +  0.00 sys =  5.25 CPU) @ 46.10/s (n=242)
       var:  5 wallclock secs ( 5.16 usr +  0.00 sys =  5.16 CPU) @ 45.93/s (n=237)

Not what I call a significant win for compiled regular expressions. Perhaps you have examples where the gain is large - I've yet to encounter them.

Abigail

Comment on Re: RegEx Perl Code Download Code

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Re: Re: RegEx Perl Code by Anonymous Monk on Jul 25, 2002 at 02:21 UTC
Perhaps you have examples where the gain is large - I've yet to encounter them. jryan's benchmark code mentioned above can be tweaked with `qr` for a significant speed optimization. Change the line `my @patterns = ('B.B', 'CB')x10;` to `my @patterns = map qr/$_/, ('B.B', 'CB')x10;` in the `&without` subroutine. Your benchmark doesn't show any support for compiled patterns, and that's due to an optimization I've already described here. Cheers, -Anomo	[reply] [d/l] [select]
Re: Re: RegEx Perl Code by jryan (Vicar) on Jul 23, 2002 at 23:14 UTC
I ran a few benchmarks here on a "contrived" large regex and large dataset; although the speed increase through qr// isn't what you'd call large, it is at least significant. Should be noted, though, that the the so-called "evil" /o was the winner in this case. At any rate, thats not to say qr// is bad. Personally, I think its great because it encourages modularity and readability in regular expressions.	[reply]
Re: RegEx Perl Code by Abigail-II (Bishop) on Jul 24, 2002 at 08:53 UTC
When I run the benchmark you are referring to, I get a slight win for "None" over "qr". Your results showed a difference of about 10% - not what I call significant. I never said `qr//` is bad. I just argued against blindly using `qr//` for no other reason than <quote>it's a good thing to do</quote>. About the only benefit I've seen from `qr//` is that it interpolates like regular expressions, and not like double quoted strings. But the interpolation is only slightly different. Abigail	[reply] [d/l] [select]