simdeez VS portable-simd

simdeez is unsafe https://docs.rs/simdeez/1.0.7/simdeez/trait.Simd.html , it's also unsound https://github.com/jackmott/simdeez/issues/47

Library | last commit to /src | remarks | |---|---| | sleef-sys | 4 years ago | Rust FFI Sleef bindings | | sleef-rs | 3 years ago | pure Rust port of Sleef | | faster | 4 years ago | No ARM support | | simdeez | 15 months ago | No ARM support (yet?) |

At some point, I decided that I wanted to accelerate the synthesis with SIMD. I started out with using packed_simd, but switched to simdeez to abstract over vector widths and enable runtime detection. However, I wanted more flexibility and the option of splitting SIMD code into multiple functions. My solution was to skip frameworks and instead use custom traits and the duplicate crate to abstract over Rust simd instrinsics for different instruction sets. I use sleef for fast sines.

Jubilee and Caleb Zulawski for their tireless work on the portable SIMD project. It will land, some day, and when it does it's going to be an amazing boon for the project.

The portable SIMD project implements an as_simd() function for slices. The basics are that you get 3 slices and the middle one is a SIMD slice. It allows for fast aligned loads of the data, which could matter if your algorithm is becoming memory bound; it is also a convenient and safe abstraction. In my case, I actually have 2 vectors (say, x and y). I can take them apart using as_simd() like so:

Rust has generics and monomorphization. You can write the algorithm once and compile for multiple targets. rust-lang/portable-simd

This Rust issue [0] was the best short summary of what an SIMD Shuffle is I could find:

„A "shuffle", in SIMD terms, takes a SIMD vector (or possibly two vectors) and a pattern of source lane indexes (usually as an immediate), and then produces a new SIMD vector where the output is the source lane values in the pattern given.“

[0] https://github.com/rust-lang/portable-simd/issues/11

Yet by default it generates code which is only compatible with Pentium4 or newer. In fact lots of serious issues relate to older CPUs and rustc developers plan is to declare them closed when they would be able to drop i686 support (all AMD CPUs which support SSE2 support x86-64, too while Intel situation is mess).

The standard API crate for portable simd is at https://github.com/rust-lang/portable-simd, but using this requires nightly, which I don't want to do. I'd like to use a crate for simd that works on both x86_64 and wasm in stable rust. wide looks fine for this purpose. Are there any potentially better choices?

See: https://github.com/rust-lang/portable-simd

As for portable SIMD, there's relatively recent activity (last commit 20 days ago) on this repository: https://github.com/rust-lang/portable-simd