System.CurrentSystemTimeZone.GetDayOfWeek C# (CSharp) Method

        private static DateTime GetDayOfWeek(int year, int month, int targetDayOfWeek, int numberOfSunday, int hour, int minute, int second, int millisecond) {
            DateTime time;
            
            if (numberOfSunday <= 4) {
                //
                // Get the (numberOfSunday)th Sunday.
                //
                
                time = new DateTime(year, month, 1, hour, minute, second, millisecond, DateTimeKind.Local);
    
                int dayOfWeek = (int)time.DayOfWeek;
                int delta = targetDayOfWeek - dayOfWeek;
                if (delta < 0) {
                    delta += 7;
                }
                delta += 7 * (numberOfSunday - 1);
    
                if (delta > 0) {
                    time = time.AddDays(delta);
                }
            } else {
                //
                // If numberOfSunday is greater than 4, we will get the last sunday.
                //
                Calendar cal = GregorianCalendar.GetDefaultInstance();            
                time = new DateTime(year, month, cal.GetDaysInMonth(year, month), hour, minute, second, millisecond, DateTimeKind.Local);
                // This is the day of week for the last day of the month.
                int dayOfWeek = (int)time.DayOfWeek;
                int delta = dayOfWeek - targetDayOfWeek;
                if (delta < 0) {
                    delta += 7;
                }
                
                if (delta > 0) {
                    time = time.AddDays(-delta);
                }
            }
            return (time);
        }

        public override DaylightTime GetDaylightChanges(int year)
        {
            if (year < 1 || year > 9999)
            {
                throw new ArgumentOutOfRangeException("year", Environment.GetResourceString("ArgumentOutOfRange_Range", (object)1, (object)9999));
            }
            object key = (object)year;

            if (!this.m_CachedDaylightChanges.Contains(key))
            {
                lock (CurrentSystemTimeZone.InternalSyncObject)
                {
                    if (!this.m_CachedDaylightChanges.Contains(key))
                    {
                        short[] local_3 = CurrentSystemTimeZone.nativeGetDaylightChanges(year);
                        if (local_3 == null)
                        {
                            this.m_CachedDaylightChanges.Add(key, (object)new DaylightTime(DateTime.MinValue, DateTime.MinValue, TimeSpan.Zero));
                        }
                        else
                        {
                            DateTime     temp_65  = CurrentSystemTimeZone.GetDayOfWeek(year, (uint)local_3[0] > 0U, (int)local_3[1], (int)local_3[2], (int)local_3[3], (int)local_3[4], (int)local_3[5], (int)local_3[6], (int)local_3[7]);
                            DateTime     local_4  = CurrentSystemTimeZone.GetDayOfWeek(year, (uint)local_3[8] > 0U, (int)local_3[9], (int)local_3[10], (int)local_3[11], (int)local_3[12], (int)local_3[13], (int)local_3[14], (int)local_3[15]);
                            TimeSpan     local_5  = new TimeSpan((long)local_3[16] * 600000000L);
                            DateTime     temp_102 = local_4;
                            TimeSpan     temp_103 = local_5;
                            DaylightTime local_6  = new DaylightTime(temp_65, temp_102, temp_103);
                            this.m_CachedDaylightChanges.Add(key, (object)local_6);
                        }
                    }
                }
            }
            return((DaylightTime)this.m_CachedDaylightChanges[key]);
        }