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

my $s = '00a0c801adc6';

timethese(100000,{
	particle => sub {
		my $str = $s;
		$str =~ s/([\w]{2})(?!$)/$1:/gio;
	},

	chipmunk => sub {
		my $str = $s;
		$str = join(':', $str =~ /../g);
	},

	petral => sub {
		my $str = $s;
		$str = join(':', split /(?=(?:..)+$)/,$str);
	},

	robot1 => sub {
		my $str = $s;
		$str = join(':', unpack 'a2a2a2a2a2a2', $str);
	},

	robot2 => sub {
		my $str = $s;
		$str = join(':', unpack('a2' x (length($str)/2), $str));
	},

});

##</code><code>##

C:\WINDOWS\Desktop>perl test_mac.pl
Benchmark: timing 100000 iterations of chipmunk, particle, petral, robot1, robot2...
  chipmunk:  3 wallclock secs ( 2.52 usr +  0.00 sys = 2.52 CPU) @ 39682.54/s (n=100000)
  particle:  6 wallclock secs ( 6.48 usr +  0.00 sys = 6.48 CPU) @ 15432.10/s (n=100000)
    petral:  5 wallclock secs ( 6.05 usr +  0.00 sys = 6.05 CPU) @ 16528.93/s (n=100000)
    robot1:  2 wallclock secs ( 1.27 usr +  0.00 sys = 1.27 CPU) @ 78740.16/s (n=100000)
    robot2:  3 wallclock secs ( 3.02 usr +  0.00 sys = 3.02 CPU) @ 33112.58/s (n=100000)