Function vcombine_u64 

pub fn vcombine_u64(a: uint64x1_t, b: uint64x1_t) -> uint64x2_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.

Join two smaller vectors into a single larger vector Arm’s documentation