def point_from_string(s)
      byte = s.bytes.first
      m = from_nibble(byte >> 4)
      x = from_nibble(byte & 0x0f)
      y = int_from_be(s[1..-1])
      [m, x, y]
    end
def point_from_string(s)
      byte = s.bytes.first
      m = from_nibble(byte >> 4)
      x = from_nibble(byte & 0x0f)
      y = int_from_be(s[1..-1])
      [m, x, y]
    end
returns [m, x, y]