in reply to Regex overlap in MAC address

0:13:46:b:4:31
^^             First pass
    ^^^^       Second pass
         ^^^   Third pass

[download]

You're expecting the regexp to match the same : twice. Use a zero-width lookahead to check for the trailing : or end of string. 

$mac =~ s/(^|:)([0-9a-fA-F])(?=:|$)/${1}0$2/g;

[download]

Better yet, eliminate needless copying. 

$mac =~ s/(^|:)(?=[0-9a-fA-F](?::|$))/${1}0/g;

[download]

Update: Tested. Fixed bug where : would get removed.

Update: If you really need speed, the following is much faster, but it sacrifices readability: 

$mac =~ s/(?<=:)(?=[0-9a-fA-F](?::|$))/0/g;
$mac =~ s/^(?=[0-9a-fA-F](?::|$))/0/;

[download]
        Rate orig fast
orig 36251/s   -- -42%
fast 62533/s  72%   --

[download]

Replies are listed 'Best First'.
Re^2: Regex overlap in MAC address
by Skeeve (Parson) on Sep 11, 2006 at 20:06 UTC
    Hi ikegami could you please rate this too? 
    $mac= join ":",map substr("00$_",-2),split/:/,$mac;

    [download]
    s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
    +.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e
[reply]
[d/l]
[select]

      Sure thing 

      use Benchmark qw( cmpthese );

our $data = '0:13:46:b:4:31';

cmpthese(-3, {
   ike_orig => 'my $mac = $data; $mac =~ s/(^|:)(?=[0-9a-fA-F](?::|$))
+/${1}0/g;               $mac;',
   ike_fast => 'my $mac = $data; $mac =~ s/(?<=:)(?=[0-9a-fA-F](?::|$)
+)/0/g;
                                 $mac =~ s/^(?=[0-9a-fA-F](?::|$))/0/;
+                        $mac;',
   skeeve   => 'my $mac = $data; $mac = join ":", map substr("0$_",-2)
+, split/:/, $mac;       $mac;',
   jwkrahn1 => 'my $mac = $data; $mac =~ s/([^:]+)/ sprintf "%02s", $1
+ /eg;                   $mac;',
   jwkrahn2 => 'my $mac = $data; $mac = join ":", map sprintf( "%02s",
+ $_ ), split /:/, $mac; $mac;',
});

      [download]
                  Rate ike_orig jwkrahn1   skeeve jwkrahn2 ike_fast
ike_orig 37908/s       --      -3%     -29%     -31%     -43%
jwkrahn1 38957/s       3%       --     -27%     -29%     -41%
skeeve   53318/s      41%      37%       --      -3%     -20%
jwkrahn2 54879/s      45%      41%       3%       --     -18%
ike_fast 66551/s      76%      71%      25%      21%       --

      [download]
[reply]
[d/l]
[select]
        Just a side note about benchmarking... It depends on the platform! See the result of your code on my Mac:
                    Rate jwkrahn1  skeeve2 jwkrahn2   skeeve ike_orig ike_fast
        jwkrahn1 49277/s       --     -11%     -15%     -17%     -20%     -50%
        skeeve2  55160/s      12%       --      -5%      -7%     -10%     -44%
        jwkrahn2 58151/s      18%       5%       --      -2%      -5%     -41%
        skeeve   59291/s      20%       7%       2%       --      -3%     -40%
        ike_orig 61250/s      24%      11%       5%       3%       --     -38%
        ike_fast 98301/s      99%      78%      69%      66%      60%       --
        s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
        +.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e
[reply]
[d/l]
[select]
        how about trying these? just playing with your fastest and adding sentinal ':'s before processing and removing them after. 
           zen3 => 'my $mac = ":".$data.":"; $mac =~ s/(?<=:)(?=[0-9a-fA-F](?:
+:))/0/g;
                                     $mac =~ s/^:|:$//; $mac;',

   zen4 => 'my $mac = ":$data:"; $mac =~ s/(?<=:)(?=[0-9a-fA-F](?::))/
+0/g;
                                 $mac =~ s/^:|:$//; $mac;',

   zen5 => 'my $mac = ":$data:"; $mac =~ s/(?<=:)(?=[0-9a-fA-F](?::))/
+0/g;
                                 $mac = substr $mac, 1,-1; $mac;',

        [download]
        my results are varied: 
                     Rate     zen2     zen3 ike_fast     zen4     zen5
zen2     152990/s       --      -1%      -1%      -4%      -6%
zen3     154915/s       1%       --      -0%      -3%      -5%
ike_fast 155051/s       1%       0%       --      -3%      -5%
zen4     159115/s       4%       3%       3%       --      -2%
zen5     162584/s       6%       5%       5%       2%       --

             Rate     zen2 ike_fast     zen4     zen3     zen5
zen2     147082/s       --      -3%      -3%      -3%      -5%
ike_fast 150866/s       3%       --      -0%      -1%      -3%
zen4     151345/s       3%       0%       --      -1%      -3%
zen3     152312/s       4%       1%       1%       --      -2%
zen5     155404/s       6%       3%       3%       2%       --

             Rate     zen2 ike_fast     zen4     zen5     zen3
zen2     132209/s       --      -1%      -4%     -10%     -13%
ike_fast 134054/s       1%       --      -3%      -9%     -11%
zen4     137554/s       4%       3%       --      -6%      -9%
zen5     147053/s      11%      10%       7%       --      -3%
zen3     151234/s      14%      13%      10%       3%       --

             Rate     zen2 ike_fast     zen3     zen4     zen5
zen2     148516/s       --      -2%      -3%      -4%      -7%
ike_fast 151827/s       2%       --      -1%      -1%      -5%
zen3     153467/s       3%       1%       --      -0%      -4%
zen4     153946/s       4%       1%       0%       --      -4%
zen5     159757/s       8%       5%       4%       4%       --

        [download]
[reply]
[d/l]
[select]

In Section Seekers of Perl Wisdom