Clarify vector_algorithms a bit

[AlexGuteniev]

by defining permutation by the macro instead of magic decimal value
if not this, then maybe let's use hex or binary constant,
but decimal is very obscure

[StephanTLavavej]

Thanks! For reference, it's xmmintrin.h that says

#define _MM_SHUFFLE(fp3,fp2,fp1,fp0) (((fp3) << 6) | ((fp2) << 4) | ((fp1) << 2) | ((fp0)))

so _MM_SHUFFLE(1, 0, 3, 2) == 78 and _MM_SHUFFLE(0, 1, 2, 3) == 27.

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

Thanks for making this magic somewhat more comprehensible! 🪄 🔮 🧠