How to rotate an SSE/AVX vector

Question

I need to perform a rotate operation with as little clock cycles as possible. In the first case let's assume __m128i as source and dest type:

source: || A0 || A1 || A2 || A3 ||

  dest: || A1 || A2 || A3 || A0 ||

dest = (__m128i)_mm_shuffle_epi32((__m128i)source, _MM_SHUFFLE(0,3,2,1));

Now I want to do the same with AVX intrinsics. So let's assume this time __m256i as source and dest type:

source: || A0 || A1 || A2 || A3 || A4 || A5 || A6 || A7 ||

  dest: || A1 || A2 || A3 || A4 || A5 || A6 || A7 || A0 ||

The AVX intrinsics is missing most of the corresponding SSE integer operations. Maybe there is some way go get the desired output working with the floating point version.

I've tried with:

dest = (__m256i)_mm256_shuffle_ps((__m256)source, (__m256)source, _MM_SHUFFLE(0,3,2,1));

but what I get is:

|| A0 || A2 || A3 || A4 || A5 || A6 || A7 || A1 ||

Any Idea on how to solve this in an efficient way? (without mixing SSE and AVX operation and without "manually" inverting A0 and A1

Thanks in advance!

Don't have much experience with SSE and AVX, but in the second line of code, if dest type is __m256, why are you casting to __m128i? — dario_ramos
Seems like all the useful instructions are in AVX2 (why didn't they release that one first?) — harold

user1584773 user1584773 · Accepted Answer · 2012-12-02T00:48:22

My solution:

__m256 tmp =  ( __m256 ) _mm256_permute_ps((__m256)_source, _MM_SHUFFLE ( 0,3,2,1 ));
* ( _dest ) =  ( __m256i) _mm256_blend_ps(tmp, _mm256_permute2f128_ps ( tmp,tmp,1 ), 136);

How to rotate an SSE/AVX vector

2 Answers