[osg-users] [ANN] Windows Binaries of OSG 3.4.0 : Visual C++ 2015 and Intel C++ 2016

[Chris Hanson]

Hey Stuart, we should coordinate.

On Thu, Apr 28, 2016 at 4:11 PM, Stuart Mentzer <osgforum at tevs.eu> wrote:

> Hi Sebastian,
>
>
> SMesserschmidt wrote:
> > Can you elaborate on the specific versions used for the 3rd-party
> libraries? Especially if you compiled against Qt and possibly which version.
>
>
> I built against Qt 5.6 and osgQt was built. I used the latest version of
> dependencies:
> curl 7.48.0
> freetype 2.6.3
> giflib 5.1.4
> glut 3.7
> libjpeg 9b
> libpng 1.6.21
> libtiff 4.0.6
> minizip GitHub tip
> zlib 1.2.8
>
>
> > Interesting, can you point to some sources why the /fp:fast is needed
> > for auto-vectorization? I'm pretty sure I've seen at least SSE2
> > vectorization on some meta-programming matrix code of mine. Precision
> > is  a real issue for me, so forgive my skepticism.
>
>
> Yes, it is hard to find the documentation on this. The "fast" option is
> required for floating point loops to fully auto-vectorize because
> vectorization can reorder operations, thus breaking strict IEEE rules.
> Similarly, if you put #pragma simd on a loop it will enable "fast" for you.
> A reference for this with VC++ is:
>
> https://blogs.msdn.microsoft.com/vcblog/2015/10/19/do-you-prefer-fast-or-precise/
> (see A7. Auto-Vectorization)
> For Intel C++ one reference is the comment by Tim P. (who knows Intel
> compilers) in:
> https://software.intel.com/en-us/forums/intel-c-compiler/topic/508146
> where he says "/fp: options other than fast prevent vectorization which
> depends on optimizing order of operations"
>
> It is probably most accurate to say that some vectorization is possible
> without the "fast" options but avoiding associativity limits vectorization.
> I'm not sure if /fp:fast=1 gives the full auto-vectorization with less
> precision loss. It would be good to have an option that allows reordering
> for loop vectorization but still uses the full precision math library
> calls, but I don't think that exists. I get the sensitivity to precision,
> which is why I'm trying to indicate that this first Intel C++ build is sort
> of experimental. Once we give it a workout and see the positive and
> negative effects of various options we'll know better what build variations
> are worth providing.
>
> Regards,
> Stuart
>
> ------------------
> Read this topic online here:
> http://forum.openscenegraph.org/viewtopic.php?p=67017#67017
>
>
>
>
>
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>



-- 
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