`func (rb *Bitmap) Rank(x uint64) uint64` is good. But I just need `Rank(end)-Rank(start)` to be `O(end-start)`, not `O(end)`
func (rb *Bitmap) Rank(x uint64) uint64is good.But I just need
Rank(end)-Rank(start)to beO(end-start), notO(end)