Announcing the Portable SIMD Project Group

posts/inside-rust/2020-09-29-Portable-SIMD-PG.md

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+---
+layout: post
+title: "Announcing the Portable SIMD Project Group"
+author: Jubilee and Lokathor
+description: "Announcing the Portable SIMD Project Group"
+team: the library team <https://www.rust-lang.org/governance/teams/library>
+---
+
+We're announcing the start of the _Portable SIMD Project Group_ within the Libs team. This group is dedicated to making a portable SIMD API available to stable Rust users.
+
+The Portable SIMD Project Group is lead by [@calebzulawski](https://github.com/calebzulawski), [@Lokathor](https://github.com/Lokathor), and [@workingjubilee](https://github.com/workingjubilee).
+
+## What are project groups?
+
+Rust uses [project groups](https://rust-lang.github.io/rfcs/2856-project-groups.html) to help coordinate work.
+They're a place for people to get involved in helping shape the parts of Rust that matter to them.
+
+## What is SIMD?
+
+SIMD stands for Single Instruction, Multiple Data.
+It lets the CPU apply a single instruction to a "vector" of data.
+The vector is a single extra-wide CPU register made of multiple "lanes" of the same data type.
+You can think of it as being *similar* to an array.
+Instead of processing each lane individually, all lanes have the same operation applied *simultaneously*.
+This lets you transform data much faster than with standard code.
+Not every problem can be accelerated with "vectorized" code, but for multimedia and list-processing applications there can be significant gains.
+
+## Why do you need to make it portable?
+
+Different chip vendors offer different SIMD instructions.
+Some of these are available in Rust's [`std::arch`](https://doc.rust-lang.org/core/arch/index.html) module.
+You *can* build vectorized functions using that, but at the cost of maintaining a different version for each CPU you want to support.
+You can also *not* write vectorized operations and hope that LLVM's optimizations will "auto-vectorize" your code.
+However, the auto-vectorizer is easily confused and can fail to optimize "obvious" vector tasks.
+
+The portable SIMD API will enable writing SIMD code just once using a high-level API.
+By explicitly communicating your intent to the compiler, it's better able to generate the best possible final code.
+This is still only a best-effort process.
+If your target doesn't support a desired operation in SIMD, the compiler will fall back to using scalar code, processing one lane at a time.
+The details of what's available depend on the build target.
+
+We intend to release the Portable SIMD API as `std::simd`.
+We will cover as many use cases as we can, but it might still be appropriate for you to use `std::arch` directly.
+For that reason the `std::simd` types will also be easily convertable to `std::arch` types where needed.
+
+## How can I get involved?
+
+Everyone can get involved!
+No previous experience necessary.
+If you'd like to help make portable SIMD a reality you can visit our [GitHub repository](https://github.com/rust-lang/project-portable-simd) or reach out on [Zulip](https://rust-lang.zulipchat.com/#narrow/stream/257879-project-portable-simd) and say hi! :wave: