use Tie::SubstrHash; tie %hash, 'Tie::SubstrHash', 7, 1, 1_000_000; print time; $hash{ pack 'A7', $_ } = ' ' for 1 .. 1_000_000; print time; 1069489311 1069489911 $n = 0; print time; $n += defined $hash{ pack 'A7', $_ } for 1 .. 1_000_000; print time, $/, $n; 1069490448 1069491023 1000000