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How best to write a cross-platform .xs module using x64 assembler?

by cnd (Acolyte)
on Mar 28, 2017 at 08:18 UTC ( #1186207=perlquestion: print w/replies, xml ) Need Help??

cnd has asked for the wisdom of the Perl Monks concerning the following question:

I wish to donate an intel chip-speed algorithm to perl users.

It works exclusively on 64bit x64 compatible CPUs (mac, windows, linux at least).

What would be the best way to make this available, and what build instructions (if any) do I need for those platforms so users can get and use my module ?

Is anyone aware of any existing assembler .xs modules that work at least on linux, preferable also mac and maybe windows ?

If anyone has suggestions for which assembler toolchains and debugging environments I should use for build pre-release testing - those would also be greatly received! Chris.

  • Comment on How best to write a cross-platform .xs module using x64 assembler?

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Re: How best to write a cross-platform .xs module using x64 assembler?
by salva (Canon) on Mar 28, 2017 at 09:37 UTC
    First write a XS/C version of your module trying to keep clearly separated what is interface to Perl (the XS side) from the code implementing the algorithm (the C side).

    Then add the assembler code inlined into the C function implementing the algorithm guarded by compiler macros so that the asm version is used on the platforms supporting it (i.e. x86_64) and the pure C on those that doesn't.

    Another approach is to include the asm version of the function in its own .S file, but then you will have to add the rules for its compilation into the Makefile. Nowadays, most perls are compiled with gcc which can also be used to compile assembler code, so it should be a relatively easy task!

    In order to detect when to use the C version or the asm version you can access the perl build configuration using Config, or in case that's not enough, you can go for Config::AutoConf.

Re: How best to write a cross-platform .xs module using x64 assembler?
by danaj (Friar) on Mar 28, 2017 at 16:39 UTC

    It's more complicated than you need, but there is some inline assembly in Math::Prime::Util. See mulmod.h and montmath.h. Basically just C code with preprocessor wrappers for different platforms.

    You can use Devel::CheckLib or similar packages for build time configuration as well.

    For testing, I recommend Linux / Unix x86 machines that match your target, an x86 that doesn't (e.g. x86 non-64), a Mac especially since they use clang which acts slightly differently than gcc (different preprocessor defines), Windows. If you're ambitious, Cygwin and a non-x86 machine.

Re: How best to write a cross-platform .xs module using x64 assembler?
by Anonymous Monk on Mar 28, 2017 at 19:45 UTC

    Is there a specific reason for it to be perl-only? Tight integration with perl internal structures?

    I would recommend rolling this up as an independent library first, if possible. Or even just a separate translation unit. The XS is best used as a thin glue.

    Are you sure that assembly is a requirement for this algorithm? Modern C compilers can autovectorize code; intrinsics are also available where needed. Furthermore, x86_64 CPUs span a number of feature-sets, beginning with just SSE3 (or is it SSE2?), going up to AVX2, and further, with miscellaneous extensions like POPCNT, BMI, FMA, and so on. Major speedups are often obtained by targeting the best feature-set.

    So it comes down the particulars of your algorithm, and how it relates to perl.

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