In Ruby1.9 is there any good way to count the number of on bits in an 
integer (after an & operation)?
Alternatively, is there any VERY light-weight implementation of a bit 
set?  I'd prefer to use Fixnums, as I'm probably going to need thousands 
of these, if the tests work out.  But before I can test, I need a decent 
bit counter.  (shift, xor, &, and | are already present for integer 
values, but I also need to count the number of "true" items after the 
logical operation.  So if a bitset is the correct approach, I'll need it 
to implement those operations, or their equivalents in terms of union 
and intersection.)

Or do I need to drop into C for this?

-- 
Charles Hixson