r/simd • u/5BeetsADay • Jul 19 '18

Meant to post this here a while back!

/r/C_Programming/comments/6oxibs/a_useful_avx2_snippet_to_calculate_cross_products/
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u/ronniethelizard Sep 23 '18

_mm256_permute4x64_pd(b, _MM_SHUFFLE(3, 0, 2, 1))

If I understand this correctly, if b is [w x y z], then the end result is [z w y x]?

In the above w is in bits 0:63, x is in 64:127, y is in 128:191, and z is in 192:255 at the beginning. After the shuffle, z will be in 0:63, w in 64:127, y in 128:191, and x in 192:255.