code: static long unassignedPrimaryFromCodePoint(int c) {
          // Create a gap before U+0000. Use c=-1 for [first unassigned].
          ++c;
          // Fourth byte: 18 values, every 14th byte value (gap of 13).
          long primary = 2 + (c % 18) * 14;
          c /= 18;
          // Third byte: 254 values.
          primary |= (2 + (c % 254)) << 8;
          c /= 254;
          // Second byte: 251 values 04..FE excluding the primary compression bytes.
          primary |= (4 + (c % 251)) << 16;
          // One lead byte covers all code points (c < 0x1182B4 = 1*251*254*18).
          return primary | ((long)UNASSIGNED_IMPLICIT_BYTE << 24);
      }
docs: Returns the unassigned-character implicit primary weight for any valid code point c.