fungsi register dan login

<?php
    //untuk register
    function register_user($nama,$pass){

        global $link;

        //mencegah sql injection
        $nama = mysqli_real_escape_string($link, $nama);
        $pass = mysqli_real_escape_string($link, $pass);

        $pass = password_hash($pass, PASSWORD_DEFAULT);
        $query = "INSERT INTO users (username, password) VALUES ('$nama','$pass')";

        if (mysqli_query($link, $query)){
            return true;
        }else{
            return false;
        }
    }

    //uji nama kembar
    function register_cek_nama($nama){
        global $link;

        $nama = mysqli_real_escape_string($link,$nama);

        $query ="SELECT * FROM users WHERE username = '$nama'";

        if ($result = mysqli_query($link, $query)) {
            if(mysqli_num_rows($result) == 0) return true;
            else return false;
        }
    }

    //untuk login
    function cek_data($nama,$pass){
        global $link;

            //mencegah sql injection
            $nama = mysqli_real_escape_string($link, $nama);
            $pass = mysqli_real_escape_string($link, $pass);

            $query = "SELECT password FROM users WHERE username='$nama'";
            $result = mysqli_query($link, $query);
            $hash   = mysqli_fetch_assoc($result)['password'];

            print_r($hash);

            // while ($data = mysqli_fetch_assoc($result)) {
            //  echo $data['password'];
            // }

        if( password_verify($pass, $hash) ){
            die('berhasil');
        }else{
            die('gagal');
        }

    }

    // function cek_data($nama , $pass){
    //  global $link;

    //      //mencegah sql injection
    //      $nama = mysqli_real_escape_string($link, $nama);
    //      $pass = mysqli_real_escape_string($link, $pass);

    //      $query = "SELECT * FROM users WHERE username = '$nama' AND password='$pass'";
    //      if($result = mysqli_query($link, $query)){
    //          if(mysqli_num_rows($result) != 0){
    //              die('berhasil');
    //          }else{
    //              die('gagal');
    //          }
    //      }


    // }
 ?>