use Benchmark qw(timethese);

use constant VALUE => 5000;
my %hash = ( 1..VALUE);

timethese(1_000_000 / VALUE, {
    'reverse' => sub {
        my %values = reverse %hash;
    },
    'map_values' => sub {
        my %values = map {$_ => undef} values %hash;
    }
});