alt Hacker News> some builtins purport to work on simd vectors but actually just unpack the vectors and do their work per-element (e.g. running `@sin()` on a `@Vector(4, f32)` will unpack the vector, run `@sin()` 4 times, and then pack it back into a vector).
this is reasonable because there isn't really a generalizable "good way" to unroll trig functions for simd. if you really care about speed youre better off implementing to the precision you care about (you might not want full precision)
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fancyfredbot • today at 8:03 PM
I bet there's a better way than unpacking, running sequentially and repacking. Even if the algorithm is very branchy you save a pack and unpack.
i don't disagree – i have my own internal vector lib of approximations and whatnot for various tradeoffs of precision and speed, so i just use those. it's just that zig has a pretty strong stance of "no unexpected/obscured code execution" so it was surprising to see a vector-capable function that was just a bunch of scalar functions in a trench coat.
maybe functions that don't actually support actual vector execution just shouldn't work on vector arguments. i also wouldn't expect `@sin()` to expand in-place out to a full cephes-like sin implementation. maybe a function call.