Magento : Product navigation (getting previous and next items)

gistfile1.php

<?php
    /**
     * Determine the previous/next link and link to current category
     */
    $_ccat        = $this->helper('catalog/data')->getCategory();
    $ppos         = $_ccat->getProductsPosition();
    $current_pid  = $this->helper('catalog/data')->getProduct()->getId();
    // build array from products positions
    $plist = array();
    foreach ($ppos as $pid => $pos) {
        $plist[] = $pid;
    }
    $curpos   = array_search($current_pid, $plist);
    // get link for prev product
    $previd   = isset($plist[$curpos+1])? $plist[$curpos+1] : $current_pid;
    $product  = Mage::getModel('catalog/product')->load($previd);
    $prevpos  = $curpos;
    while (!$product->isVisibleInCatalog()) {
        $prevpos += 1;
        $nextid   = isset($plist[$prevpos])? $plist[$prevpos] : $current_pid;
        $product  = Mage::getModel('catalog/product')->load($nextid);
    }
    $prev_url = $product->getProductUrl();
    // get link for next product
    $nextid   = isset($plist[$curpos-1])? $plist[$curpos-1] : $current_pid;
    $product  = Mage::getModel('catalog/product')->load($nextid);
    $nextpos  = $curpos;
    while (!$product->isVisibleInCatalog()) {
        $nextpos -= 1;
        $nextid   = isset($plist[$nextpos])? $plist[$nextpos] : $current_pid;
        $product  = Mage::getModel('catalog/product')->load($nextid);
    }
    $next_url = $product->getProductUrl();
    // get link for current category
    $more_url = $_ccat->getUrl(); 
?>