def reverse_byte_pairs!
      w = ""
      w.force_encoding("BINARY") if w.respond_to?(:force_encoding)
      (0...@bytes.size).step(2) do |i|
        w << @bytes[i+1]
        w << @bytes[i]
      end
      @bytes = w
      __setobj__ @bytes
      self
  end
def reverse_byte_pairs!
      w = ""
      w.force_encoding("BINARY") if w.respond_to?(:force_encoding)
      (0...@bytes.size).step(2) do |i|
        w << @bytes[i+1]
        w << @bytes[i]
      end
      @bytes = w
      __setobj__ @bytes
      self
  end
reverse the order of bytes in 16-bit words