README.md
1# The Rust standard library's portable SIMD API
2
3
4Code repository for the [Portable SIMD Project Group](https://github.com/rust-lang/project-portable-simd).
5Please refer to [CONTRIBUTING.md](./CONTRIBUTING.md) for our contributing guidelines.
6
7The docs for this crate are published from the main branch.
8You can [read them here][docs].
9
10If you have questions about SIMD, we have begun writing a [guide][simd-guide].
11We can also be found on [Zulip][zulip-project-portable-simd].
12
13If you are interested in support for a specific architecture, you may want [stdarch] instead.
14
15## Hello World
16
17Now 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
18
19```bash
20rustup update -- nightly
21```
22
23or by setting up `rustup default nightly` or else with `cargo +nightly {build,test,run}`. After updating, run
24```bash
25cargo new hellosimd
26```
27to create a new crate. Finally write this in `src/main.rs`:
28```rust
29#![feature(portable_simd)]
30use std::simd::f32x4;
31fn main() {
32 let a = f32x4::splat(10.0);
33 let b = f32x4::from_array([1.0, 2.0, 3.0, 4.0]);
34 println!("{:?}", a + b);
35}
36```
37
38Explanation: 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]`.
39
40## Supported vectors
41
42Currently, vectors may have up to 64 elements, but aliases are provided only up to 512-bit vectors.
43
44Depending 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.
45
46The supported element types are as follows:
47* **Floating Point:** `f32`, `f64`
48* **Signed Integers:** `i8`, `i16`, `i32`, `i64`, `isize` (`i128` excluded)
49* **Unsigned Integers:** `u8`, `u16`, `u32`, `u64`, `usize` (`u128` excluded)
50* **Pointers:** `*const T` and `*mut T` (zero-sized metadata only)
51* **Masks:** 8-bit, 16-bit, 32-bit, 64-bit, and `usize`-sized masks
52
53Floating point, signed integers, unsigned integers, and pointers are the [primitive types](https://doc.rust-lang.org/core/primitive/index.html) you're already used to.
54The mask types have elements that are "truthy" values, like `bool`, but have an unspecified layout because different architectures prefer different layouts for mask types.
55
56[simd-guide]: ./beginners-guide.md
57[zulip-project-portable-simd]: https://rust-lang.zulipchat.com/#narrow/stream/257879-project-portable-simd
58[stdarch]: https://github.com/rust-lang/stdarch
59[docs]: https://rust-lang.github.io/portable-simd/core_simd
60
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