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Comment by curiouscoding | Hacker News Reader

Anything in particular that threw you off? I'd be happy to add a few words to briefly explain some of the less intuitive rust syntax.

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Nah just the final bits, stuff like `Simd::<u32, 8>::splat(q)`, I'm not sure what splatting is or how Rust's Simd library works or, admittedly, how SIMD works in detail at all. So eg I'm not sure what that 8 is doing there in the type parameters, details like that. Maybe this isn't a Rust thing but a SIMD thing, btw, I don't know much Rust but I also never wrote any SIMD code ever. I don't know how the article could be clearer, IMO once you go into the deep nitty gritty optimization stuff you just gotta assume the reader knows the tools you're using. I'm OK with dropping out halfway cause the core idea is there even before you squeeze out all the perf.

`Simd::<u32, 8>` is describing a vector with 8 lanes, where the width of each lane is 32-bits. For targets that support it, that should get you a 256-bit register.

The `splat(q)` constructor is just saying, "populate each lane with `q`." That is, the value is "splatted" across every lane in the vector.

The main idea of SIMD is simple: you represent multiple points of data in the same register and use specialized CPU instructions to operate on those points simultaneously. The difficulty of SIMD is coming up with clever algorithms that use the available instructions in an efficient way.

Ahh right, I've been doing too much TypeScript lately. I thought a type parameter couldn't impact behavior but only typechecking but clearly in Rust (like in C++) it can. Thanks for the explanation!

Ah so splat is like a memset for the entire vector to the same value. OK makes sense, I bet that wasn't actually a Rust-ism at all, just basic SIMD lingo I didn't know. Thanks again!

It's the Intel intrinsic `_mm256_set1_epi32()` except with an amusing name. Got to give Rust the win here.

wow yeah, i way prefer Rust's notation there! but i assume you could make a similar zero-cost abstraction with some mildly crazy C++ template programming.

Nice to see other real experts (and a bit of celebrities) in here.

(For the uninitiated: Burntsushi of ripgrep fame.)

yeah tbh i was a bit starstruck that burntsushi would reply to my comment explaining what i assume is utter SIMD basics. that must be how swifties feel when she (or, likelier, her PR drones) click "like" on their insta comments.

Does burntsushi have PR drones (who can explain SIMD)? :)

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