$ perl 1099601.pl
                 Rate       reverse reverse_noref       regular      keysonly
reverse        2222/s            --          -35%          -93%          -93%
reverse_noref  3406/s           53%            --          -89%          -89%
regular       31693/s         1326%          830%            --           -0%
keysonly      31726/s         1328%          831%            0%            --
$