[WordPress] shortlink

function add_head_shortlink(){
	global $post;
	if ( is_singular() ) {
		$siteurl = trailingslashit(get_option('siteurl'));
		$hex_id = dechex($post->ID);
		echo "<link rel=\"shortlink\" href=\"$siteurl$hex_id\" />\n";
	}
}
add_action('wp_head', 'add_head_shortlink');

function redirect_shortlink($redirect_url, $requested_url){
	if ( !empty($redirect_url) ) return $redirect_url;

	$siteurl = trailingslashit(get_option('siteurl'));
	$pattern = '/' . preg_quote($siteurl, '/') . '([\da-f]+)$/i';
	if ( preg_match_all( $pattern, $requested_url, $matches ) ) {
		$post_id = $matches[1][0];
		$redirect_url = get_permalink(hexdec($post_id));
		if ( empty($redirect_url) ) $redirect_url = get_permalink($post_id);
	}

	return $redirect_url;
};
add_filter('redirect_canonical', 'redirect_shortlink', 10, 2 );