Some of you may have wondered why I didn't just benchmark it myself. Because I was being stupid. I looked at tedv's benchmark and couldn't believe I hadn't bothered to check. Blame it on over two-weeks straight of working without a day off :(

A critical portion of regex optmization is what occurs on failure. I created a string which had at least one failure for the regex and then benchmarked the comparisons:

#!/usr/bin/perl -w
use strict;
use Benchmark;

my ( $re, $test );

timethese(-30, {
    regex1  => '$re = "a" . \'\d\'x500 . "a";
                $test = ("a"x2000 . "1"x499)x2 . "a" . "1"x500 . ("a"x
+2000 . "1"x499)x2 ;
                $test =~ /$re/o;',
    regex2  => '$re = "a" . \'\d{500}\' . "a";
                $test = ("a"x2000 . "1"x499)x2 . "a" . "1"x500 . ("a"x
+2000 . "1"x499)x2 ;
                $test =~ /$re/o;',
});
[download]

Results:

Benchmark: running regex1, regex2, each for at least 30 CPU seconds...
    regex1: 31 wallclock secs (31.31 usr +  0.00 sys = 31.31 CPU) @ 65
+5.10/s (n=20508)
    regex2: 31 wallclock secs (30.84 usr +  0.00 sys = 30.84 CPU) @ 53
+0.35/s (n=16358)
[download]

After running this a couple of times, I see that \d{2} is less efficient than \d\d, though not by much. If there is terribly convoluted data I am iterating over, though, it could be an issue.

I still don't see why I didn't benchmark it before asking. Thanks for slapping sense into me, tedv :)

Cheers,
Ovid

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