rrr, a compressed representation of a binary sequence providing
constant time rank and logarithmic time select operations in
nH_o(B) + o(n) bits as described in

Rajeev Raman, Venkatesh Raman, and Srinivasa Rao Satti. Succinct
indexable dictionaries with applications to encoding k-ary trees,
prefix sums and multisets. ACM Transactions on Algorithms, 3(4), 2007.

Francisco Claude and Gonzalo Navarro. Practical rank/select queries
over arbitrary sequences. In Proc. 15th International Symposium on
String Processing and Information Retrieval (SPIRE’08), volume 5280 of
Lecture Notes in Computer Science, pages 176–187, 2009.

Gonzalo Navarro and Eliana Providel. Fast, small, simple rank/select
on bitmaps. In Experimental Algorithms, volume 7276 of Lecture Notes
in Computer Science, pages 295–306. 2012.