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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] sse asin implementation
- From: Gael Guennebaud <gael.guennebaud@xxxxxxxxx>
- Date: Thu, 2 Apr 2009 08:32:06 +0200
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On Thu, Apr 2, 2009 at 6:20 AM, Jitse Niesen <jitse@xxxxxxxxxxxxxxxxx> wrote:
> On Wed, 1 Apr 2009, Gael Guennebaud wrote:
>
>> let me remind that currently the packet versions of sin, cos, exp, log
>> and sqrt are enabled by default (regardless of the fast-math option).
>> The vectorized version of sin, cos and sqrt can be disabled by
>> defining a preprocessor token. If there are good argument I'm still ok
>> to change this behavior for "disabled by default" and "enabled if
>> either EIGEN_FAST_MATH or _FAST_MATH_ are defined".
>
> I did not follow the previous discussion about the sse implementation of
> sqrt in detail, but I believe the conclusion was that we're willing to lose
> one or two bits of precision. That's probably no problem in the vast
> majority of cases. However, it's against the IEEE floating point standard,
> which says that sqrt should be computed to full precision. Thus, this is
> what I'd expect sqrt to do in the default case. Of course, you may decide
> otherwise, but at least stick a fat warning in the documentation.
>
> I'm not sure how relevant this is to your question. Perhaps not very.
it is relevant. Since I'm fine with both behavior I need people
express their opinion to make that change or not. So I count one vote
to "disable by default unless -ffast-math is set".
> Incidentally, Eigen/src/Core/GenericPacketMath.h:197 reads
>
> template<typename Packet> inline static Packet ei_psqrt(Packet a)
> { return ei_log(a); }
>
> It seems weird to call ei_log in the body ...
oops, fixed in rev 948062, thanks a lot.
> Cheers,
> Jitse
>
>
>