public static int DaysInMonth(int year, int month)
{
    if (month < 1 || month > 12)
    {
        throw new ArgumentOutOfRangeException("month", Environment.GetResourceString("ArgumentOutOfRange_Month"));
    }
    int[] arg_32_0 = DateTime.IsLeapYear(year) ? DateTime.DaysToMonth366 : DateTime.DaysToMonth365;
    int[] array = arg_32_0;
    return array[month] - array[month - 1];
}

public static bool IsLeapYear(int year)
{
    if (year < 1 || year > 9999)
    {
        throw new ArgumentOutOfRangeException("year", Environment.GetResourceString("ArgumentOutOfRange_Year"));
    }
    if (year % 4 != 0)
    {
        return false;
    }
    if (year % 100 != 0)
    {
        return true;
    }
    return year % 400 == 0;
}

private static readonly int[] DaysToMonth365 = {
0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365};
private static readonly int[] DaysToMonth366 = {
0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366};