The existence of platform specific hacks is not interesting. In reality what happens is that software which has at any point cared about being portable doesn't use them.

But yes stdc_count_ones is indeed the intrinsic you'd want here, and only a few years after I stopped writing C, so thanks for mentioning that.

std::popcount is C++ but it's also kinda miserable that it took until C++ 20 and yet they still only landed the unsigned integer types, even though C++ 20 also insists the signed integers have two's complement representation, so the signed integers do have these desirable properties in fact but you can't use that.

> In reality what happens is that software which has at any point cared about being portable doesn't use them.

I don't think this generalization is actually true. Fast portable software compiles conditionally based on the target platform, picking the fast platform-specific intrinsic, and falls back to a slow but guaranteed portable software implementation. This pattern is widespread in numerical linear algebra, media codecs, data compressors, encryption, graphics, etc.

Maybe we are just quibbling over semantics but the compiler intrinsic here is '__builtin_popcount'. 'stdc_count_ones' is a standard library element that presumably will be implemented using the intrinsic.

And FWIW all major C/C++ have for a long time have had a an intrinsic for this. In clang it even has the same name, Visual Studio it's something like just '_popcount'. So it has long been easy to roll your own macro that works everywhere.

__builtin_popcount is not platform specific.