I need display posts on same category in links next and previous posts.

I tried this code what I found:

$post_id = $post->ID; // current post id
$cat = get_the_category();
$current_cat_id = $cat[0]->cat_ID; // current category Id 

$args = array('category'=>$current_cat_id,'orderby'=>'post_date','order'=> 'DESC');
$posts = get_posts($args);
// get ids of posts retrieved from get_posts
$ids = array();
foreach ($posts as $thepost) {
    $ids[] = $thepost->ID;
}
// get and echo previous and next post in the same category
$thisindex = array_search($post->ID, $ids);
$previd = $ids[$thisindex-1];
$nextid = $ids[$thisindex+1];

if (!empty($previd)){
?>
<a rel="prev" href="<?php echo get_permalink($previd) ?>">Previous</a>
<?php
}
if (!empty($nextid)){
?>
<a rel="next" href="<?php echo get_permalink($nextid) ?>">Next</a>
<?php
}
?>

I use theme twenty twelve and I have put this code in single.php. Apparently this code do the job, but it only rotate 5 posts not all post in category.

Any advice will be welcome. Thanks