#! perl
use strict;
use warnings;
use Benchmark qw(cmpthese);

my $source = '37 35 37 8 17 16 25 36 37 3840 42 42 42 40';
my $target = '37 35 37 8 17 16 25 36 37 38 40 42 42 42 40';

cmpthese
(
    1e8,
    {
        capture    => capture   ($source),
        lookaround => lookaround($source),
    }
);

sub capture
{
    my ($line) = @_;
    $line =~ s/([0-9]{2})([0-9]{2})/$1 $2/g;
    die unless $line eq $target;
}

sub lookaround
{
    my ($line) = @_;
    $line =~ s/(?<=[0-9]{2})(?=[0-9]{2})/ /g;
    die unless $line eq $target;
}
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