code: private static int utf8Read3(int cu1, int cu2, int cu3) {
      if ((cu2 & 0xC0) != 0x80) {
        return INVALID;
      }
      if (cu1 == 0xE0 && cu2 < 0xA0) {
        // overlong
        return INVALID;
      }
      if ((cu3 & 0xC0) != 0x80) {
        return INVALID;
      }
      return (cu1 << 12) + (cu2 << 6) + cu3 - 0xE2080;
    }
docs: Read a 3 byte UTF8 sequence.
  
  @return the resulting code point or {@link #INVALID} if invalid.