9ccc7b78ec
Add `size_of` and `size_of_val` and `align_of` and `align_of_val` to the prelude (Note: need to update the PR to add `align_of` and `align_of_val`, and remove the second commit with the myriad changes to appease the lint.) Many, many projects use `size_of` to get the size of a type. However, it's also often equally easy to hardcode a size (e.g. `8` instead of `size_of::<u64>()`). Minimizing friction in the use of `size_of` helps ensure that people use it and make code more self-documenting. The name `size_of` is unambiguous: the name alone, without any prefix or path, is self-explanatory and unmistakeable for any other functionality. Adding it to the prelude cannot produce any name conflicts, as any local definition will silently shadow the one from the prelude. Thus, we don't need to wait for a new edition prelude to add it. |
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| beginners-guide.md | ||
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| CONTRIBUTING.md | ||
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| README.md | ||
The Rust standard library's portable SIMD API
Code repository for the Portable SIMD Project Group. Please refer to CONTRIBUTING.md for our contributing guidelines.
The docs for this crate are published from the main branch. You can read them here.
If you have questions about SIMD, we have begun writing a guide. We can also be found on Zulip.
If you are interested in support for a specific architecture, you may want stdarch instead.
Hello World
Now we're gonna dip our toes into this world with a small SIMD "Hello, World!" example. Make sure your compiler is up to date and using nightly. We can do that by running
rustup update -- nightly
or by setting up rustup default nightly or else with cargo +nightly {build,test,run}. After updating, run
cargo new hellosimd
to create a new crate. Finally write this in src/main.rs:
#![feature(portable_simd)]
use std::simd::f32x4;
fn main() {
let a = f32x4::splat(10.0);
let b = f32x4::from_array([1.0, 2.0, 3.0, 4.0]);
println!("{:?}", a + b);
}
Explanation: We construct our SIMD vectors with methods like splat or from_array. Next, we can use operators like + on them, and the appropriate SIMD instructions will be carried out. When we run cargo run you should get [11.0, 12.0, 13.0, 14.0].
Supported vectors
Currently, vectors may have up to 64 elements, but aliases are provided only up to 512-bit vectors.
Depending on the size of the primitive type, the number of lanes the vector will have varies. For example, 128-bit vectors have four f32 lanes and two f64 lanes.
The supported element types are as follows:
- Floating Point:
f32,f64 - Signed Integers:
i8,i16,i32,i64,isize(i128excluded) - Unsigned Integers:
u8,u16,u32,u64,usize(u128excluded) - Pointers:
*const Tand*mut T(zero-sized metadata only) - Masks: 8-bit, 16-bit, 32-bit, 64-bit, and
usize-sized masks
Floating point, signed integers, unsigned integers, and pointers are the primitive types you're already used to.
The mask types have elements that are "truthy" values, like bool, but have an unspecified layout because different architectures prefer different layouts for mask types.