get_comment_id_fields( int $id )

function get_comment_id_fields( $id = 0 ) {
	if ( empty( $id ) )
		$id = get_the_ID();

	$replytoid = isset($_GET['replytocom']) ? (int) $_GET['replytocom'] : 0;
	$result  = "<input type='hidden' name='comment_post_ID' value='$id' id='comment_post_ID' />\n";
	$result .= "<input type='hidden' name='comment_parent' id='comment_parent' value='$replytoid' />\n";

	/**
	 * Filters the returned comment id fields.
	 *
	 * @since WP-3.0.0
	 *
	 * @param string $result    The HTML-formatted hidden id field comment elements.
	 * @param int    $id        The post ID.
	 * @param int    $replytoid The id of the comment being replied to.
	 */
	return apply_filters( 'comment_id_fields', $result, $id, $replytoid );
}