Re: [boost] Review Request : Boost.SIMD

Subject: Re: [boost] Review Request : Boost.SIMD
From: Jason Roehm (jasonr_at_[hidden])
Date: 2017-02-10 15:25:50

On 02/10/2017 02:45 AM, Joel FALCOU via Boost wrote:
> Thanks for your interest.
>
>> The documentation looks good. May I ask one or two things?
>>
>> 1. Is simd::pack a POD? i.e. can aligned memory be cast into a pack?
>>
>> float* aligned_memory=...;
>> simd::pack<float>* packed_memory = (simd::pack<float>*) aligned_memory;
>>
>> (this would make my experiment a two-line change)
>
> It is. We however advise using our load/aligned_load functions so you 
> can access more fine-tuned operations and we can guarantee that the 
> proper intrinsic are emitted. We had cases where such reintrepret_cast 
> lead to subtle bugs on some compilers/arch combination or sub-optimal 
> performances.

Does Boost.SIMD support non-aligned loads/stores? Aligned data is ideal, 
but having the ability to load/store from addresses that aren't aligned 
(and emitting the appropriate instructions to do so safely, e.g. 
_mm_loadu_ps() instead of _mm_load_ps() with SSE) can be important for 
some applications also. That would allow the use of SIMD without having 
to do an explicit realignment first. On some architectures (e.g. 
post-Nehalem x86 CPUs with SSE), the aligned/unaligned penalty is very 
small also.

The library looks very good in my cursory glance over the documentation; 
I'm looking forward to see it get a review.

Jason