Function vext_p8 

pub fn vext_p8(a: poly8x8_t, b: poly8x8_t, const N: i32) -> poly8x8_t

Available on (AArch64 or ARM64EC) and (AArch64 or ARM64EC or target feature v7) and (ARM or AArch64 or ARM64EC) and target feature neon only.

Extract vector from pair of vectors Arm’s documentation