Assuming these are date objects, start at $fromdate, add one day to it, until that date is Sunday, and as long as the date is before $todate. Add 7 days to each Sunday you find, add that date and continue as long as the new date is before $todate. Keep track of each date found this way.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…