[Proj] Experiment to speed up proj.4 by 2 or more

[José Luis García Pallero]

2015-06-23 18:30 GMT+02:00 Even Rouault <even.rouault at spatialys.com>:
> José Luis,
>
>>
>> 1. Introducing C++: From my point of view, one of the PROJ best things
>> is that it is written in pure C.
>
> In which respect is the actual implementation of proj important to you as a
> user, if you can still use it as a C library ? All nowadays C compilers should
> be able to deal with C++ as well, and here I'm only using C++98 features (I'd
> even say C++83 ;-)), not C++14.
>
> The code compiles with at least back to gcc 4.1 (generated code not optimal
> however), which is really ancient. It doesn't compile with gcc 3.4, but this
> is not because of the C++ part, but lack of support for SSE2 intrinsics.

OK, there is no problem if the library can still be used as a C library

>
>> Also I can see in the SLEEF folder
>> that there exists a folder called 'purec'
>
> Yes, but don't use that one as it is a software emulation of the
> transcendantal functions, that opearte on single double arguments, and that
> has roughly the same performance of standard non-SIMD x87 functions.
>
> The SIMD sleef implementation itself is .c/.h. The C++ bits I added in the
> equation is just to make the code more readable, since using the sleef C
> functions, or directly the Intel intrinsics, would rather be ugly. Do you
> prefer a + b (C++) or vadd_vd_vd_vd(a,b) (SLEEF) or _mm_add_pd(a,b) (Intel
> intrinsics) ? You can just compare the 2 source files of my P.O.C to see the
> benefit of relying on C++ overloaded arithmetic operators (I'm far from being a
> big C++ lover, but that's one of the use cases where it is undoubtly
> appropriate)
>
>> 2. Can be used SLEEF with Intel compilers, PathScale, Portland et al.?
>
> Intel compiler, yes (according to SLEEF doc). No idea for the others (never
> heard about them actually), but I guess that if they're decent enough and have
> support for the SIMD intrinsics, that should work.
>
> Even
>
> --
> Spatialys - Geospatial professional services
> http://www.spatialys.com



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