gistfile1.PL

my @last_days = (
    undef,
    sub { 31 },
    sub { my $y = shift; return $y % 4 or not ($y % 100) 28 : 29 },
    sub { 31 },
    sub { 30 },
    sub { 31 },
    sub { 30 },
    sub { 31 },
    sub { 31 },
    sub { 30 },
    sub { 31 },
    sub { 30 },
    sub { 31 },
);

my $last_day = $last_days[$month]->($year);