std::bitset

Seems like std::bitset<N> under the hood is an array of unsigned longs now, this means that there will be an (heavy?) overhead when N is small. sizeof(std::bitset<8>) is 8 bytes!

Is there a reason why the type of underlying array itself is not a template parameter? Why does the implementation not use uint32_t/16_t/8_t when more appropriate? I do not see anything in the implementation that limits this?

I am guessing I am missing a particular reason but unsure how to look for it or maybe there is no reason at all ? Since this is such a simple container I am not able to understand how the zero overhead principle of C++ seems to be avoided here.

GCC Impl: https://gcc.gnu.org/onlinedocs/gcc-4.6.2/libstdc++/api/a00775_source.html

I believe clang is similar (used sizeof to confirm)