sub v6 {
    %subs = ();
    $subs{$&}++ while $string =~ m{A{2,}|C{2,}|G{2,}|T{2,}}g;
    } # v6

##</code><code>##

      Rate   v4   v5   v6
v4 55470/s   --  -9% -39%
v5 60734/s   9%   -- -34%
v6 91365/s  65%  50%   --