code: static long getThreeBytePrimaryForOffsetData(int c, long dataCE) {
          long p = dataCE >>> 32;  // three-byte primary pppppp00
          int lower32 = (int)dataCE;  // base code point b & step s: bbbbbbss (bit 7: isCompressible)
          int offset = (c - (lower32 >> 8)) * (lower32 & 0x7f);  // delta * increment
          boolean isCompressible = (lower32 & 0x80) != 0;
          return Collation.incThreeBytePrimaryByOffset(p, isCompressible, offset);
      }
docs: Computes a 3-byte primary for c's OFFSET_TAG data "CE".