http://3cbzkrvakrpetjjppdwzbzqrlkmzatjs7jbyazap5gwutj32gcltjpqd.onion
However: None of them were faster than the normal double-loop.
And I think (but never found the energy to try to positively
prove) that comes down to an edge case: If there's not a single
bit set in the 64-bit window, we need to handle that specially.