I 100% agree with this part :) I'm glad you noted it explicitly somewhere, as this trick should be better known. Note that while sparse, it is not as memory ef

I 100% agree with this part :) I'm glad you noted it explicitly somewhere, as this trick should be better known. Note that while sparse, it is not as memory efficient as, for example, linked list bitmaps. This is because the mask is going to contain O(universe/wordsize) bits, and depending on the size of the universe, the mask may be larger than the actual data stored!