Rust u8数组转u64

fn as_u64_le(u: &[u8]) -> u64 {
    ((u[0] as u64) << 0)
    | ((u[1] as u64) << 8)
    | ((u[2] as u64) << 16)
    | ((u[3] as u64) << 24)
    | ((u[4] as u64) << 32)
    | ((u[5] as u64) << 40)
    | ((u[6] as u64) << 48)
    | ((u[7] as u64) << 56)
}