Function _mm_alignr_epi8 

pub fn _mm_alignr_epi8(a: __m128i, b: __m128i, const IMM8: i32) -> __m128i

Available on x86-64 and target feature ssse3 only.

Concatenate 16-byte blocks in a and b into a 32-byte temporary result, shift the result right by n bytes, and returns the low 16 bytes.

Intel’s documentation