一个当前日期求周数的问题~~~~~~~~~

根据下面的方法，周的起始是周日，而不是周一，怎么改动，让他周一到周日为一周，而不是周日到周六/// 求当前日期是一年的中第几周        
/// </summary>         
/// <param name="date"></param>       
/// <returns></returns>   
public static int WeekOfYear(DateTime curDay)     
    { int firstdayofweek = Convert.ToInt32(Convert.ToDateTime(curDay.Year.ToString() + "- " + "1-1 ").DayOfWeek);             
     int days = curDay.DayOfYear;         
     int daysOutOneWeek = days - (7 - firstdayofweek);              
      if (daysOutOneWeek <= 0)          
   { 
 return 1;
}             
else            
{                
 int weeks = daysOutOneWeek / 7;       
   
 if (daysOutOneWeek % 7 != 0)            
         weeks++;             
    return weeks + 1;               }