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;        }