Multiversion

Function multiversioning attribute macros for Rust.

What is function multiversioning?

Many CPU architectures have a variety of instruction set extensions that provide additional functionality. Common examples are single instruction, multiple data (SIMD) extensions such as SSE and AVX on x86/x86-64 and NEON on ARM/AArch64. When available, these extended features can provide significant speed improvements to some functions. These optional features cannot be haphazardly compiled into programs--executing an unsupported instruction will result in a crash.

Function multiversioning is the practice of compiling multiple versions of a function with various features enabled and safely detecting which version to use at runtime.

Features

• Dynamic dispatching, using runtime CPU feature detection
• Static dispatching, avoiding repeated feature detection for nested multiversioned functions (and allowing inlining!)
• Support for generic and async functions

Limitations

• No support for member functions or associated functions (or any other functions not at module-level)
• No support for impl Trait

Example

Automatic function multiversioning with the target_clones attribute, similar to GCC's target_clones attribute: ```rust use multiversion::target_clones;

[targetclones("[x86|x8664]+avx", "x86+sse")]

fn square(x: &mut [f32]) { for v in x { *v *= *v; } } ```

Manual function multiversioning with the multiversion and target attributes: ```rust use multiversion::{multiversion, target};

[target("[x86|x86_64]+avx")]

unsafe fn square_avx(x: &mut [f32]) { for v in x { *v *= *v; } }

[target("x86+sse")]

unsafe fn square_sse(x: &mut [f32]) { for v in x { *v *= *v; } }

[multiversion(

"[x86|x86_64]+avx" => unsafe square_avx,
"x86+sse" => unsafe square_sse

)] fn square(x: &mut [f32]) { for v in x { *v *= *v; } } ```

License

Multiversion is distributed under the terms of both the MIT license and the Apache License (Version 2.0).

See LICENSE-APACHE and LICENSE-MIT for details.