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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] Vectorized quaternion multiplication.
- From: Rohit Garg <rpg.314@xxxxxxxxx>
- Date: Sat, 7 Mar 2009 17:49:59 +0530
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I think that the scalar version loses out because the multiplies are
not pipelined there.
On Sat, Mar 7, 2009 at 5:30 PM, Rohit Garg <rpg.314@xxxxxxxxx> wrote:
> When you put it in, please tell me. :)
>
> I posted this for feedback here and you may be interested.
>
> http://forum.beyond3d.com/showthread.php?t=52840
>
> On Sat, Mar 7, 2009 at 5:16 PM, Gael Guennebaud
> <gael.guennebaud@xxxxxxxxx> wrote:
>> hi,
>>
>> thanks a lot,
>>
>> at a first glance I was not sure about the perf, because it needs a
>> lot of shuffle instructions which are quite costly, so benched, and on
>> my core2 your version is 1.5 times faster :) Then I changed the
>> shuffle_ps for the simpler PSHUFD instr. and now, it is almost 2x
>> faster, so really worth it :)
>>
>> FYI I only changed vec4f_swizzle like this:
>>
>> #define vec4f_swizzle(v,p,q,r,s) (_mm_castsi128_ps(_mm_shuffle_epi32(
>> _mm_castps_si128(v), \
>> ((s)<<6|(r)<<4|(q)<<2|(p)))))
>
> Now I see. This instruction takes one operand alone so is perhaps
> faster (aka higher throughput).
>
> --
> Rohit Garg
>
> http://rpg-314.blogspot.com/
>
> Senior Undergraduate
> Department of Physics
> Indian Institute of Technology
> Bombay
>
--
Rohit Garg
http://rpg-314.blogspot.com/
Senior Undergraduate
Department of Physics
Indian Institute of Technology
Bombay