Reddit Ranking Algorithms in PHP

Ranking.php

<?php
/**
 * Ranking Library
 * contains alogrithms for story ranking
 * Basically a PHP Implementation of reddits algorithms
 *
 * @author      Lucas Nolte <lnolte@i.biz>
 * @since       0.1
 * @package     Polska Wiadomosc
 * @subpackage  Libraries
 * @see         https://github.com/reddit/reddit/blob/master/r2/r2/lib/db/_sorts.pyx
 */
class Ranking {
    
    /**
     * calculates the score for a link (upvotes - downvotes)
     * 
     * @access  private
     * @since   0.1
     * @param   int $upvotes, int $downvotes
     * @return  int
     */
    private function _score($upvotes = 0, $downvotes = 0) {
        return $upvotes - $downvotes;
    }
    
    /**
     * calculates the hotness of an article
     * 
     * @access  private
     * @since   0.1
     * @param   int $upvotes, int $downvotes, int $posted
     * @return  float
     */
    private function _hotness($upvotes = 0, $downvotes = 0, $posted = 0) {
        $s = $this->_score($upvotes, $downvotes);
        $order = log(max(abs($s), 1), 10);
        
        if($s > 0) {
            $sign = 1;
        } elseif($s < 0) {
            $sign = -1;
        } else {
            $sign = 0;
        }
        
        $seconds = $posted - 1134028003;
        
        return round($order + (($sign * $seconds)/45000), 7);
    }
    
    /**
     *  confidence sort based on http://www.evanmiller.org/how-not-to-sort-by-average-rating.html
     * 
     * @since   0.1
     * @access  private
     * @param   int $upvotes, int $downvotes
     * @return  double
     * @see     http://www.evanmiller.org/how-not-to-sort-by-average-rating.html
     */
    private function _confidence($upvotes = 0, $downvotes = 0) {
        $n = $upvotes + $downvotes;
        
        if($n === 0) {
            return 0;
        }
        
        $z = 1.281551565545; // 80% confidence
        $p = floor($upvotes) / $n;
        
        $left = $p + 1/(2*$n)*$z*$z;
        $right = $z*sqrt($p*(1-$p)/$n + $z*$z/(4*$n*$n));
        $under = 1+1/$n*$z*$z;
        
        return ($left - $right) / $under;
    }
    
    /**
     * calculates the controversy score for a link
     * 
     * @since   0.1
     * @param   int $upvotes, int $downvotes
     * @access  public
     * @return  float
     */
    public function controversy($upvotes = 0, $downvotes = 0) {
        return ($upvotes + $downvotes) / max(abs($this->_score($upvotes, $downvotes)), 1);
    }
    
    /**
     * public method to calculate a post's hotness
     * 
     * @since   0.1
     * @param   int $upvotes, int $downvotes, int $posted
     * @access  public
     * @return  float
     */
    public function hotness($upvotes, $downvotes, $posted) {
        return $this->_hotness($upvotes, $downvotes, $posted);
    }
    
    /**
     * public method to calculate a posts confidence
     * 
     * @since   0.1
     * @param   int $upvotes, int $downvotes
     * @access  public
     * @return  double
     */
    public function confidence($upvotes, $downvotes) {
        return $this->_confidence($upvotes, $downvotes);
    }
}

What about using$order = log10(max(abs($s), 1)); instead of log()

Do you have an example ussage?

Where are the upvotes and downvotes sourced from? Is it just from the post, or do comments get factored in somehow?

My hunch is that only the immediate children of a post or top-level comment are counted in ranking that entity. But it would be nice to get confirmation from someone who has been on the team at some point.