c#里 DateTime加（减）上N个工作日（不包括周未）

public DateTime addWorkDays(DateTime dt,int addDays)
        {
            DateTime dtStart = dt;
            DateTime dtEnd = dtStart.AddDays(-addDays);
            int days = CalculateWeekendDays(dtStart,dtEnd);
            while(days>0)
            {
                dtStart = dtEnd;
                dtEnd = dtEnd.AddDays(-days);
                days = CalculateWeekendDays(dtStart,dtEnd);
            }
            return dtEnd;
        }

        public  int CalculateWeekendDays(DateTime  dtStart,  DateTime dtEnd)
        {
            int  count=0;
            for(DateTime  dtTemp = dtStart;dtTemp > dtEnd;dtTemp = dtTemp.AddDays(-1))
            {
                if(dtTemp.DayOfWeek==DayOfWeek.Saturday||dtTemp.DayOfWeek==DayOfWeek.Sunday)
                {
                    count++;
                }
            }
            return  count;
        }