Function vaddhn_s64 

pub fn vaddhn_s64(a: int64x2_t, b: int64x2_t) -> int32x2_t

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

Add returning High Narrow. Arm’s documentation