[janwas]

I beg to differ :) std::experimental::simd has a very limited set of operations: mostly just math, very few shuffles/swizzles. Last I checked, it also only worked in a recent version of GCC.

We do indeed have cross-platform intrinsics here: github.com/google/highway. Disclosure: I am the main author.

[an1sotropy]

cool; thanks for pointing out your project!

Do you have any advice on how someone limited to c99/c11 can still leverage the wisdom and techniques inside it?

[janwas]

:) Tricky. Is it an option to build some source files with C++, and use C functions (the usual FFI) as the interface between them?

[an1sotropy]

Not really, unfortunately, and it’s a pre-existing framework for teaching a class, so simplicity of compilation is extra important. Also if I try to isolate the SIMD bits in C++ I’ll lose the opportunity to have them be inlined which will defeat the optimization purpose.

For those that are new to this, can you give an example of a kind of computation or algorithm which is well-served by your project, but not possible with vector extensions like https://clang.llvm.org/docs/LanguageExtensions.html#vectors-... ?

[janwas]

> Also if I try to isolate the SIMD bits in C++ I’ll lose the opportunity to have them be inlined which will defeat the optimization purpose.

Agreed. Usually the interface would be something like RunEntireAlgorithm(), not DotProduct().

> For those that are new to this, can you give an example of a kind of computation or algorithm which is well-served by your project but not possible with vector extensions

Sure. Vector extensions are OKish for simple math but JPEG XL includes nontrivial cross-lane operations such as transpose and boundary handling for convolution. __builtin_shufflevector requires a known vector length, and can be pessimized (fusing two into one general all-to-all permute which is more expensive than two simple shuffles).

Also, vqsort (https://github.com/google/highway/tree/master/hwy/contrib/so...) almost entirely consists of operations not supported by the extensions, and actually works out of the box on variable-length RISC-V and SVE, which compiler extensions cannot.

[an1sotropy]

This is very helpful; thank you.