Re: [eigen] Issues regarding Quaternion-alignment and const Maps

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

Benoit Jacob wrote:
> I have made a patch letting ei_pset1 use _mm_loaddup_pd when we have SSE3:
>
> template<> EIGEN_STRONG_INLINE Packet2d ei_pset1<double>(const double&  from) {
> #ifdef EIGEN_VECTORIZE_SSE3
>   return _mm_loaddup_pd(&from);
> #else
>   Packet2d res = _mm_set_sd(from);
>   return ei_vec2d_swizzle1(res, 0, 0);
> #endif
> }
>
> But guess what? It's actually not faster (perhaps even a bit slower)
> than our ei_vec2d_swizzle1!
>
> So let's just forget about it.
>
> Christoph, is  _mm_loaddup_pd the only SSE3 intrinsic your code is
> using ? If yes, by using ei_pset1 instead of _mm_loaddup_pd, you can
> make your code work on SSE2 !

I guess the most important SSE3 instruction is _mm_addsub_pd which adds 
the first and subtracts the second element. If there is a code which 
negates just one element, this could be replaced.

Googleing a bit implies that the SSE-way to do it is to XOR with
{-0.0, 0.0} (or the other way around). I will try that ...

Christoph

--
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Dipl.-Inf. Christoph Hertzberg
Cartesium 0.051
Universität Bremen
Enrique-Schmidt-Straße 5
28359 Bremen

Tel: (+49) 421-218-64252
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