Add conversions for Simd from/to arrays of types convertible from/to Simd

[programmerjake]

as suggested in https://rust-lang.zulipchat.com/#narrow/channel/257879-project-portable-simd/topic/q2p8affineqb.20and.20double-pumping/near/521157051

[programmerjake]

So, @calebzulawski @workingjubilee do you think having the conversions be fully generic over anything that implements Into is a good idea, or should we limit that to arrays, Simd and the platform-specific SIMD types? Is this good enough to merge?

[calebzulawski]

The thing I'm not particularly liking is the dimension change preventing a nice generic implementation. Not that it means we shouldn't implement this, but is this conversion supported by bytemuck?

[programmerjake]

The thing I'm not particularly liking is the dimension change preventing a nice generic implementation.

yeah, but since generic const exprs isn't coming anytime soon, imo this is the best we can do.

Not that it means we shouldn't implement this, but is this conversion supported by bytemuck?

Simd is not supported by bytemuck 1.23.0 (latest)
turns out it actually is supported, you just need to enable the nightly_portable_simd feature that's not enabled by default on docs.rs.

[workingjubilee]

This doesn't seem like quite the right solution.

[programmerjake]

This doesn't seem like quite the right solution.

ok, so then do you have any better ideas, or can you be more specific? imo something like this would be quite useful, so we should have some better way (preferably safe) than just a manual mem::transmute

[calebzulawski]

Maybe something that uses arrays as an intermediate and relies on optimization (since transmutes don't care about alignment, right?)