Add _MM_SHUFFLE macro for x86/x86_64

[bitshifter]

xmmintrin.h defines a _MM_SHUFFLE macro which is use to generate the mask used for _mm_shuffle and other similar instructions. https://clang.llvm.org/doxygen/xmmintrin_8h.html#a65a052b655bd49ff3fe128b61847df9f. I could not find this macro in std::arch::x86, perhaps it is there but doesn't show up in the docs?

In any case, if it's missing perhaps it would be good to add it. Creating masks by hand is cryptic and having an equivalent to _MM_SHUFFLE would make using the Rust intrinsics more like other languages.

[gnzlbg]

Thanks for reporting this. Wanna send a PR? Should be pretty easy to implement (check the other macros and consts in the coresimd/x86/sse.rs module.

[bitshifter]

Will do.

[bitshifter]

@gnzlbg it turns out this is not so straight forward. I've added the macro and a test in this commit bitshifter@727bc11 however it seems that coresimd is re-exported via stdsimd, but I do not know how to re-export the macro.

I was reminded about binary literals when looking at the tests, which are reasonably readable. Perhaps if this macro issue is not easily solved adding and boolean literal example would help.

[gnzlbg]

@bitshifter you should add a const fn instead of a macro, or why does it need to be a macro?

[gnzlbg]

Also, you should call it _MM_SHUFFLE and not _mm_shuffle.

[gnzlbg]

Otherwise it looks good!