How to identify when the home page is the current one?

I’m making a horizontal menu using the wp_list_pages() function; it returns the css tag “current_page_item” if the user is on a particular page, in addition to the tag “page_item”.

But is there a way to find out if the user is not on a page at all, i.e. on the home page or viewing posts? How do I know if the home page is the current one?

Thanks.
–Alex