adduser_process.php not adding information to MySQL table
<form name="adduser_form" action="process/adduser_process.php" method="post">
    Username:<input id="username" type="test" name="username" />
    Email:<input id="email" type="text" name="email" />
    Password:<input id="password" type="password" name="password" />
    <input id="add_usr" type="button" value="Add User" onclick="formhash(this.form, this.form.password);" />
</form>

function formhash(form, password) {
    var p = document.createElement("input");
    form.appendChild(p);
    p.name = "p";
    p.type = "hidden";
    p.value = hex_sha512(password.value);
    password.value = "";
    form.submit();
}

include '../includes/lgn_connect.php';
include '../includes/functions.php';
sec_session_start();

$password = $_POST['p'];

$random_salt = hash('sha512', uniqid(mt_rand(1, mt_getrandmax()), true));

$password = hash('sha512', $password.$random_salt);

if($insert_stmt = $mysqli->prepare("INSERT INTO users (username, email, password, salt) VALUES (?, ?, ?, ?)")) {
$insert_stmt->bind_param('ssss', $username, $email, $password, $random_salt);

$insert_stmt->execute();
}

<input id="username" type="test" name="username" />     //should be
<input id="username" type="text" name="username" />

if($insert_stmt = $mysqli->prepare("INSERT INTO users (username, email, password, salt) VALUES (?, ?, ?, ?)"))   //should be

if(($insert_stmt = $mysqli->prepare("INSERT INTO users (username, email, password, salt) VALUES (?, ?, ?, ?)")))

session_start();