# File mconv.rb, line 189
  def Mconv.minimize_charset(charset, string)
    # shortcut
    if /\A(?:euc-jp|utf-8|iso-8859-1)\z/i =~ charset
      if /\A[\x00-\x7f]*\z/ =~ string
        return 'us-ascii'
      else
        return charset
      end
    end

    charset2 = 'us-ascii'
    begin
      # round trip?
      s2 = Iconv.conv(charset, charset2, Iconv.conv(charset2, charset, string))
      return charset2 if string == s2
    rescue Iconv::Failure
    end
    charset
  end