Source

File: wp-includes/comment.php

function get_comment_pages_count( $comments = null, $per_page = null, $threaded = null ) {
	global $wp_query;

	if ( null === $comments && null === $per_page && null === $threaded && ! empty( $wp_query->max_num_comment_pages ) ) {
		return $wp_query->max_num_comment_pages;
	}

	if ( ( ! $comments || ! is_array( $comments ) ) && ! empty( $wp_query->comments ) ) {
		$comments = $wp_query->comments;
	}

	if ( empty( $comments ) ) {
		return 0;
	}

	if ( ! get_option( 'page_comments' ) ) {
		return 1;
	}

	if ( ! isset( $per_page ) ) {
		$per_page = (int) get_query_var( 'comments_per_page' );
	}
	if ( 0 === $per_page ) {
		$per_page = (int) get_option( 'comments_per_page' );
	}
	if ( 0 === $per_page ) {
		return 1;
	}

	if ( ! isset( $threaded ) ) {
		$threaded = get_option( 'thread_comments' );
	}

	if ( $threaded ) {
		$walker = new Walker_Comment;
		$count  = ceil( $walker->get_number_of_root_elements( $comments ) / $per_page );
	} else {
		$count = ceil( count( $comments ) / $per_page );
	}

	return $count;
}