libCat VS highway

That's awesome! I'm working on something that sounds similar. https://github.com/cons-cat/libcat

I'd love to see your work if you're willing to share it here!

This runtime size bothers me a lot. So much that I've been working on a new runtime for C++ that breaks POSIX compatibility to keep binaries as small as they can be. The hello world with LTO is 330ish bytes right now, and I think that can get smaller. https://github.com/Cons-Cat/libCat

I'm working on a library that replaces both C++ and C/POSIX standard libraries (https://github.com/Cons-Cat/libCat), but even then I need to define a few std:: namespace symbols for some features. In the case of std::initializer_list, my answer is just don't use that feature, because you don't really need it.

It's worse in the standard library than it has to be. When I refactored my traits to minimize template instantiations and lean on concepts as much as possible, I measured over 30% improvement to clean build compile times. It's not possible for the standard to do this, because it would subtly change the API. For instance, you can't instantiate or take the address of a concept, but you can for a type-trait class. No reason you'd want to do that, but you can, so they can't "break" the standard library by optimizing this.

This doesn't have to be true. Over the past year I've made progress towards demonstrating how even non-freestanding C++ can be written without any C or C++ standard library headers or DLLs (with large benefits). There are a few names which the compilers require to be in the std:: namespace, though, but they're very special features like source_location and construct_at with semantics that can't be expressed otherwise.

This bit cast has no overhead in debug mode, and is a little bit more generally useful than std::bit_cast(), but cannot be constant evaluated. https://github.com/Cons-Cat/libCat/blob/main/src/libraries/utility/implementations/bit_cast.tpp

It isn't that hard to put a predicate into a type. We have lambdas in an unevaluated context, CTAD, and templated type aliases. https://github.com/Cons-Cat/libCat/blob/main/src/libraries/scaredy/cat/scaredy https://github.com/Cons-Cat/libCat/blob/main/src/global_includes.hpp#L70 https://github.com/Cons-Cat/libCat/blob/main/src/libraries/linux/cat/linux#L289 You do it like this.

But suppose that you have code with no standard library calls at all. Would it still make sense to choose this naming convention? This is actually possible, with a few special exceptions. GCC requires that an implementation of std::source_location has very particular class member names, GCC assigns special semantics to a few function names including std::construct_at and std::move (people seem to know it's inlined, but did you know std::move is required for move-related warnings?), and most intrusively of all, a promise_type must be snake_case. Other names can be worked around by using them into a different namespace with a different letter-case, but promise_type seems unavoidable.

I use C++ for a low-level Linux runtime. Other people are using it for operating systems like SerenityOS and Zircon/Fuschia. People also use C++ for making more compilers like GCC and LLVM.

GitHub

It's great you bring up cmp, helps to understand why 4x128 is not necessarily as good as 1x512. Quicksort, hardly a 'weird kernel', does comparisons followed by compaction. Because comparisons return a predicate, which have only a single write port, we can only do 128 bits of comparisons per cycle. Ouch.

However, masking can still help our VQSort [1], for example when writing the rightmost partition right to left without stomping on subsequent elements, or in a sorting network, only updating every second element.

[1] https://github.com/google/highway/tree/master/hwy/contrib/so...

The bf16 dot instruction replaces 6 instructions: https://github.com/google/highway/blob/master/hwy/ops/x86_12...

[0] for those interested in Highway.

It's also mentioned in [1], which starts off

> Today we're sharing open source code that can sort arrays of numbers about ten times as fast as the C++ std::sort, and outperforms state of the art architecture-specific algorithms, while being portable across all modern CPU architectures. Below we discuss how we achieved this.

[0] https://github.com/google/highway

[1] https://opensource.googleblog.com/2022/06/Vectorized%20and%2..., which has an associated paper at https://arxiv.org/pdf/2205.05982.pdf.

Thanks so much!

Everyone working on this self-selected into contributing, so I think of it less as my team than ... a team?

Specifically want to call out: Jan Wassenberg (author of https://github.com/google/highway) and I started gemma.cpp as a small project just a few months ago + Phil Culliton, Dan Zheng, and Paul Chang + of course the GDM Gemma team.

C++ users can enjoy Highway [1].

[1] https://github.com/google/highway/

At that point it is better to have some kind of DSL that should not be in the main language, because it would target a much lower level than a typical program. The best effort I've seen in this scene was Google's Highway [1] (not to be confused with HighwayHash) and I even once attempted to recreate it in Rust, but it is still distanced from my ideal.

[1] https://github.com/google/highway