Problem with this approach is that you have to create intput Vector<bool> argument first, which is likely to spoil any benefits from faster Bits...

Really, this is the issue - to improve speed here, the interface is problem.

Some possible solutions that came to my mind:

void Bits::Set(int pos, int count, dword bits);

Here count <= 32 and you are passing values in bits dword; that would work if you are packing some normal data into Bits.

template
void Bits::Set(int pos, int count, auto lambda /* [=] (int pos) -> bool */)

Here we would provide lambda that returns value for given position - if compiler is good, it should inline well.

tempalte
void Bits::Set(int pos, bool x ...)

Maybe vararg template is a possible solution to the problem too.

Now the question is: How are you using Bits?

Mirek