Yes exactly. Do a bitwise AND / OR, and count the number of bits that are set. From this count, you can estimate the number of entries in the set: https://en.wi

Yes exactly. Do a bitwise AND / OR, and count the number of bits that are set. From this count, you can estimate the number of entries in the set: https://en.wikipedia.org/wiki/Bloom_filter#Approximating_the_number_of_items_in_a_Bloom_filter https://en.wikipedia.org/wiki/Bloom_filter#Approximating_the... HyperLogLog (and variants) can do the union part as well, and need much less space than Bloom filters thought. For large sets, that is. For cardinality smaller than e.g. 100, Bloom filters are better.