code: func OverflowShardBits(rowID int64, shardRowIDBits uint64) bool {
  	mask := (1<<shardRowIDBits - 1) << (64 - shardRowIDBits - 1)
  	return rowID&int64(mask) > 0
  }
docs: // OverflowShardBits checks whether the rowID overflow `1<<(64-shardRowIDBits-1) -1`.