nordic-dev.net/rust
nordic-dev.net/rust
2
0
Fork 0
mirror of https://github.com/rust-lang/rust.git synced 2024-11-22 14:55:26 +00:00
Code Issues Packages Projects Releases Wiki Activity

Resolve https://github.com/rust-lang/stdsimd/pull/8#discussion_r495583060

Browse Source
This commit is contained in:
Lokathor 2020-09-27 10:27:24 -06:00
parent 0ac2ee32cf
commit 656312e33c
1 changed files with 1 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
beginners-guide.md
View File

@ -19,7 +19,7 @@ SIMD has a few special vocabulary terms you should know:
* **Vector:** A SIMD value is called a vector. This shouldn't be confused with the `Vec<T>` type. A SIMD vector has a fixed size, known at compile time. All of the elements within the vector are of the same type. This makes vectors *similar to* arrays. One difference is that a vector is generally aligned to its *entire* size (eg: 16 bytes, 32 bytes, etc), not just the size of an individual element. Sometimes vector data is called "packed" data.
* **Lane:** A single element position within a vector is called a lane. If you have `N` lanes available then they're numbered from `0` to `N-1` when referring to them, again like an array. The biggest difference between an array element and a vector lane is that it is *relatively costly* to access an individual lane value. Generally, the vector has to be pushed out of register onto the stack, then an individual lane is accessed while it's on the stack. For this reason, when working with SIMD you should avoid reading or writing the value of an individual lane during hot loops.
* **Lane:** A single element position within a vector is called a lane. If you have `N` lanes available then they're numbered from `0` to `N-1` when referring to them, again like an array. The biggest difference between an array element and a vector lane is that in general is *relatively costly* to access an individual lane value. On most architectures, the vector has to be pushed out of the SIMD register onto the stack, then an individual lane is accessed while it's on the stack (and possibly the stack value is read back into a register). For this reason, when working with SIMD you should avoid reading or writing the value of an individual lane during hot loops.
* **Bit Widths:** When talking about SIMD, the bit widths used are the bit size of the vectors involved, *not* the individual elements. So "128-bit SIMD" has 128-bit vectors, and that might be `f32x4`, `i32x4`, `i16x8`, or other variations. While 128-bit SIMD is the most common, there's also 64-bit, 256-bit, and even 512-bit on the newest CPUs.