gp featured post excerpt length

by 
// gp blog - featured post excerpt length
add_filter( 'excerpt_length', function( $length ) {
    global $wp_query;
    if ( 0 === $wp_query->current_post && !wp_is_mobile() ) {
        // Set Length of first post on desktop
        $length = 50;
    } else {
        // Set Length of other posts and all posts on mobile
        $length = 20;
    }
	return $length;
}, 200);