sub check_reps {
    my ($pwd) = @_;

    while ($pwd =~ /(?=((.+)\2+))/g) {
        printf "%s repeated %d times, covers %d%%\n",
            $2,
            length($1) / length($2),
            100 * length($1) / length($pwd)
        ;
    }
}

check_reps('xattattttatty');

__END__
att repeated 2 times, covers 46%
ttatt repeated 2 times, covers 76%
tt repeated 2 times, covers 30%
t repeated 3 times, covers 23%
t repeated 2 times, covers 15%
t repeated 2 times, covers 15%