use Benchmark qw/ cmpthese /;
my $x = 42.0;
my $y = "$x";
my $p = pack 'F', $x;
my (%h1,%h2,%h3,%h4);
cmpthese( -1, {
    F => sub { $h1{ pack 'F', $x } = 1 },
    s => sub { $h2{ $x }           = 1 },
    y => sub { $h3{ $y }           = 1 },
    p => sub { $h4{ $p }           = 1 },
});

__END__

        Rate    s    F    p    y
s  4032984/s   -- -64% -84% -84%
F 11327209/s 181%   -- -54% -56%
p 24707825/s 513% 118%   --  -5%
y 25997751/s 545% 130%   5%   --