How many times does a day occur within a date range?

Given two dates I need to know how many times each day of the week occurs within that range, so that I can calculate a value where the factor varies by day.  So I wrote the following code which returns an array of integers, position 0 will tell you how many Sundays there are, position 6 will tell you how many Saturdays, and so on.

int[] CountDays(DateTime firstDate, DateTime lastDate)
{
  var totalDays = lastDate.Date.Subtract(firstDate.Date).TotalDays + 1;
  var weeks = (int)Math.Floor(totalDays / 7);

  var result = Enumerable.Repeat<int>(weeks, 7).ToArray();
  if (totalDays % 7 != 0)
  {
    int firstDayOfWeek = (int)firstDate.DayOfWeek;
    int lastDayOfWeek = (int)lastDate.DayOfWeek;
    if (lastDayOfWeek < firstDayOfWeek)
      lastDayOfWeek += 7;
    for (int dayOfWeek = firstDayOfWeek; dayOfWeek <= lastDayOfWeek; dayOfWeek++)
      result[dayOfWeek % 7]++;
  }
  return result;
}