If you have a known large number N of items to insert up front, and future inserts will be random, you can do the reindexing to 2^64 / N in advance. (Perhaps th

If you have a known large number N of items to insert up front, and future inserts will be random, you can do the reindexing to 2^64 / N in advance. (Perhaps there's a further optimization in rounding N up to the next power of 2). N = 2^48 is what gives you his strategy of numbering the initial entries in increments of 65536.