B4R Code Snippet Day of week calculation

I'd like to share this Sub, for calculation the day of week, based on Zeller's algorithm

Private Sub weekday(day As Int, month As Int, year As Int) As Int


    Dim dayofweek As Int ' day of week
    month = month -2
    If month = -1 Then
        month = 11
    End If
    If month = 0 Then
        month = 12
    End If
    Dim c As Int = Floor(year/100)
    Dim d As Int = year - c*100

    Dim f As Int = day + (Floor(13*month-1)/5) +d+ Floor(d/4) +Floor(d/4)-2*c
    dayofweek = f Mod 7
    If dayofweek < 0 Then dayofweek=dayofweek + 7 'Sunday = 0
    Return dayofweek
End Sub

Hope this is useful to somebody