Re: [eigen] Intermediate Packet Storage

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I'm no ARM expert, but I assume {d{2k}-d{2k+1}} is an alias for `q{k}`


As I mentioned, my project requires GCC 5. I would be interested to know if newer versions of ARM GCC have the same issue - but there seems to be some issue with Eigen on newer versions, because godbolt is giving me errors.

Yes, I have no idea about what causes this -- maybe some ARM expert can chip in.

Thinking about it, I suppose the question is how to get an ARM SIMD (e.g. int32x4_t) in to/out of a POD int32_t[4] array.

At the moment, Eigen implements this in NEON pload/ploudu using these intrinsics:

And for storing:

So, if Eigen uses these intrinsics, I guess it's no surprise that this results in the intructions we see. The problem is that I don't know how else to load/store an int32x4_t into POD without using these intrinsics.

Perhaps there is a way.

Are you able to implement the above (or something similar) with pure intrinsics?

Yes - the intermediate would be stored in a float32x4_t register in each of these cases.

> If that is not possible, I'd see no way at all to do this with that
> compiler. If it is possible, I'd see some hope in implementing the
> previously mentioned Meta-Packets.

I guess one thought would be the syntax inspired by std::placeholders, and boost::lambda:

using Eigen = E;
y = x.bind((E::_1 > 0.0f).select(E::sin(E::_1), E::cos(E::_1));

And if there were combined with std::tie inspired syntax you could do multi-assignment one-liners:

E::tie(x, y) = E::tie(E::cos(a), E::cos(b))
    .bind(E::_1 + E::_2, E::_1 - E::2);

Just a thought!

Thanks for you thoughts.

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