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Subject: Re: [Boost-users] POD 3d vectors
From: Mike Marchywka (marchywka_at_[hidden])
Date: 2009-05-29 22:11:24

> Date: Fri, 29 May 2009 18:40:46 -0500
> From:
> To: boost-users_at_[hidden]
> Subject: Re: [Boost-users] POD 3d vectors
> On Fri, May 29, 2009 at 5:49 PM, tom fogal wrote:
>> gtsml owevwr writes:
>>> I need fast low dimensional vector (2, 3 and 4 dimension let say).
>> Still, you probably want to search around a bit more first. Without
>> checking, I'd bet all of CrystalSpace, Ogre, VTK, Irrlicht, and
>> random google result for "open source 3d engine" here> include their
>> own classes for vectors and matrices.

Fast usually depends on access patterns as lookahead or cache thrashing or VM limits
the speed. These off course tend to be app or algorithm specific but if someone wanted
to catagorize and parameterize these maybe you could make some general
strategy paterns for optimum performance on different platforms but you can
appreciate it could be involved. I still often use int[] for arbitrary
"vectors" depending on need and often various simple types of encoding
( keeping smaller differences than absolute values ) can make some sense.
So, it is easy to find reasons to reinvent your own wheels in this case.
I can write a low dimensional add operator easily, I can't go through library
code and yank out extra junk. You could probably get at more speed
issues from increasing the locality of an algorithm rather than looking for the library
with the best vector add code.

Mike Marchywka
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