weeknum

# File lib/date.rb, line 1519
  def self.weeknum(y=1582, w=41, d=5, f=0, h=0, min=0, s=0, of=0, sg=ITALY) # :nodoc:
    unless (jd = valid_weeknum?(y, w, d, f, sg)) &&
           (fr = valid_time?(h, min, s))
      raise ArgumentError, 'invalid date'
    end
    if String === of
      of = (zone_to_diff(of) || 0).to_r/86400
    end
    new!(jd_to_ajd(jd, fr, of), of, sg)
  end