title: Efficient way of iterating over true bits in std::bitset?
body: <p>Is there a way of iterating over a (possibly huge) <code>std::bitset</code> that is <em>linear</em> in the <em>number of bits that are set to true</em>? I want to prevent having to check every single position in the bitset. The iteration should successively return the indices of each bit that is set to true.</p>