SIMD ideas for Rust

[bearophile]

Manu:

> //    return [arb[0] - aib[0], arb[1] + aib[1]]; // this final 
> line is
> tricky... it's not very portable.
>
>     // Maybe:
>     return select([-1, 0], arb-aib, arb+aib);
>     // Hopefully the x86 optimiser will generate the proper 
> opcode. Or a
> bunch of other options; a multi-vector shuffle, shift, swizzle, 
> interleave.
> }
>
> I think that would be better. More portable, and it eliminates 
> the code
> that implies a vector->float->vector cast sequence, which I 
> maintain,
> should be syntactically discouraged at all costs.
> You don't want to be giving people bad ideas that it's 
> reasonable code to
> write ;)

Apparently that select() uses __builtin_ia32_pblendvb128, that is 
a SSE4.1 instruction. At the moment I have only SSE3 :-(

Bye,
bearophile