Can go furthr and convert to digit array by parts, and stream those parts, this way can avoid sllocations altogether.

But this would be more complex change

I think this is plenty - large bitsets are increasingly uncommon, and anyone touching iostreams isn't going to have great perf in the first place.

anyone touching iostreams isn't going to have great perf in the first place

Well, stringstream is not as that, but generally agree.

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

Thanks for letting the allocator take some vacation days! 🏖️ 🥳 😹