Function vget_low_s64 

pub fn vget_low_s64(a: int64x2_t) -> int64x1_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.

Duplicate vector element to vector or scalar Arm’s documentation