Find the WordPress root directory from any child directory by using PHP

Today I try to built a TinyMCE plugin with a custom dialog, and I like to dialog to be integrated with the WordPress APIs.

In order to find out the WordPress root directory I have write the following function

function get_wp_root()
{
    $depth          =   0;
    $current_path   =   __DIR__;

    while(!file_exists($current_path . DIRECTORY_SEPARATOR . 'wp-config.php'))
    {
        ++$depth;
        $current_path   =   dirname($current_path);

        if($depth > 20)
        {
            break;
        }
    }

    return $current_path;
}

I hope this helps :)