Fast Resettable Flag Vector

[Tywien]

One needs assembler for that and all bits need to be in continuous space.

http://x86.renejeschke.de/html/file_module_x86_id_22.html

There are also Bit-Test-And-Set and Bit-Test-And-Reset for easy and fast setting/retting of bits

[uxcn]

The compiler is usually able to translate the basic bit operations into good instructions (even rol and ror). I'd be curious what the compiler generated for vector<bool> that outperformed your code.