You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: rand_custom.rs
    path of file: ./repos/smartcore/src
    
    the code of the file until where you have to start completion: #[cfg(not(feature = "std_rand"))]
pub use rand::rngs::SmallRng as RngImpl;
#[cfg(feature = "std_rand")]
pub use rand::rngs::StdRng as RngImpl;
use rand::SeedableRng;

/// Custom switch for random fuctions
pub fn get_rng_impl(seed: Option<u64>) -> RngImpl {
    match seed {
        Some(seed) => RngImpl::seed_from_u64(seed),
        None => {
            cfg_if::cfg_if! {
                if #[cfg(feature = "std_rand")] {
                    use rand::RngCore;
                    RngImpl::seed_from_u64(rand::thread_rng().next_u64())
                } else {
                    // no std_random feature build, use getrandom
                    #[cfg(feature = "js")]
                    {
                        let mut buf = [0u8; 64];
                        getrandom::getrandom(&mut buf).unwrap();
                        RngImpl::seed_from_u64(buf
    
pub fn get_rng_impl(seed: Option<u64>) -> RngImpl {
    match seed {
        Some(seed) => RngImpl::seed_from_u64(seed),
        None => {
            cfg_if::cfg_if! {
                if #[cfg(feature = "std_rand")] {
                    use rand::RngCore;
                    RngImpl::seed_from_u64(rand::thread_rng().next_u64())
                } else {
                    // no std_random feature build, use getrandom
                    #[cfg(feature = "js")]
                    {
                        let mut buf = [0u8; 64];
                        getrandom::getrandom(&mut buf).unwrap();
                        RngImpl::seed_from_u64(buf[0] as u64)
                    }
                    #[cfg(not(feature = "js"))]
                    {
                        // Using 0 as default seed
                        RngImpl::seed_from_u64(0)
                    }
                }
            }
        }
    }
}