__m512i _bswap endianness in C/C++?

[c_s_]

This might be a noob question, but is there a way to perform a byte swap between big and little endian on a __m512i vector without having to iterate through each value? I really want to avoid using unions, as they can be slow. I can't find any info in documentation or googling around, so hopefully somebody here can help me.

[Kevin_D_Intel]

I'm checking with our Developer. Stay tuned.

[Kevin_D_Intel]

Developer's guidance is that vector byte swap is not available as there is no hardware support for it.

Let me know if you have additional questions.

[jimdempseyatthecove]

Look at using _mm256_shuffle_epi8

This will work on AVX2, I haven't checked to see if this is supported on Phi. As long as the byte swaps do not cross 128-bit lanes, this will work for you. You will also have to check to see if this disturbs the high 256-bits. This will affect your strategy to perform 512-bit byte endian shuffle.

Jim Dempsey

[SergeyKostrov]

>>...I really want to avoid using unions, as they can be slow... Almost all Intel's intrinsic data types are union based ( there are just a couple of exceptions when they declared as structs ) and if you have some performance issues more technical details need to be provided.

[James_C_9]

you can read in the data to vector as byte, then use swizzle to swap the elements (bytes),  then write back the vector.  This only do 16 bytes at a time, though.  Reading in full full 64 bytes and swap the bytes by shifts and bit or/and may actually be faster.

[Charles_C_Intel1]

@Jim:  Xeon Phi (Knight's Corner) doesn't support any MMX, SSE*, or AVX* flavors.  So __mm256 instructions can't be used.   Sorry

Charles

[Patrick_S_]

You could just write your own byte swap routine involving the bitwise logical and shift __m512i operations.

The relevant functions are listed under AVX-512... I didn't test it, but i guess they should also work on KNC. There are a lot of functions not listed under AVX-512, but still work on KNC...

http://software.intel.com/sites/landingpage/IntrinsicsGuide/