@rddt = (1) x 1000;
$pond = 32;

Benchmark::cmpthese(500, {
   'inside' => sub { 
            for ( my $i = 64 ; $i < ( scalar(@rddt) - ( 2 * $pond ) ) ; $i++ ) {
               $x++;
            }
               },

   'outside' => sub {
            $limit = scalar(@rddt) - ( 2 * $pond );
            for ( my $i = 64 ; $i <  $limit ; $i++ ) {
               $x++;
            }
               },
});

inside  273/s      --    -39%
outside 450/s     65%      --