code: func packChunkID(seriesID, chunkID uint64) uint64 {
  	if seriesID > (1<<40)-1 {
  		panic("series ID exceeds 5 bytes")
  	}
  	if chunkID > (1<<24)-1 {
  		panic("chunk ID exceeds 3 bytes")
  	}
  	return (seriesID << 24) | chunkID
  }
docs: // packChunkID packs a seriesID and a chunkID within it into a global 8 byte ID.
  // It panicks if the seriesID exceeds 5 bytes or the chunk ID 3 bytes.