What is the source code for page navigation in php

Check this code snippet
[PHP]
<?php
//If you use it, please link to my site
$full_path = getenv("REQUEST_URI");
//put the base URL in case you need it
$base = "http://subomain.domain.ext";
//Get the name of the file
$page_file = basename($full_path);
//The files are named file_1.php, file_2.php, etc. Extract number from it.
$page_num = substr($page_file
, strrpos($page_file, "_") + 1
, strpos($page_file, ".php") - strrpos($page_file, "_") - 1
);
$partial_path = substr($page_file, 0, strrpos($page_file, "_"));
//Build array of pagenumbers. Here are ten pages.
$all_pages = array (1,2,3,4,5,6,7,8,9,10);
foreach ($all_pages as $all_page)
{
//Create link to all the previus pages and put in prev-image.
if ($all_page < $page_num)
{
print "<a rel='nofollow' href="$partial_path"."_". $all_page . ".php"><img src="images/prev.gif" alt="$all_page" border="0"></a>";
}
//Create I-am-here-image.
elseif ($all_page == $page_num)
{
print "<img src="images/here.gif" alt="$page_num" border="0">";
}
//Create links to all the next pages and put in next-image.
else
{
print "<a rel='nofollow' href="$partial_path"."_" . $all_page . ".php"><img src="images/next.gif" alt="$all_page" border="0"></a>";
}
}
?>
[/PHP]