# File lib/filesize.rb, line 134
    def from(arg)
      parts  = parse(arg)
      prefix = parts[:prefix]
      size   = parts[:size]
      type   = parts[:type]

      raise ArgumentError, "Unparseable filesize: #{arg}" unless type

      offset = (type[:prefixes].map { |s| s[0].chr.downcase }.index(prefix.downcase) || -1) + 1

      new(size * (type[:multiplier] ** (offset)), type)
    end