Universe.php

/**
 * Generating 1.000.000 solar systems (3 iterations).
 * Chances for a 6 star solar system are fairly small.
 * Only one solar system with 6 stars out of 3 million.
 *
 * #1st
 *   1 Star : 732724
 *   2 Stars: 234559
 *   3 Stars: 30955
 *   4 Stars: 1728
 *   5 Stars: 34
 *   6 Stars: 0
 *
 * #2nd
 *   1 Star : 731628
 *   2 Stars: 235170
 *   3 Stars: 31506
 *   4 Stars: 1657
 *   5 Stars: 39
 *   6 Stars: 0
 *
 * #3rd
 *   1 Star : 732048
 *   2 Stars: 234795
 *   3 Stars: 31363
 *   4 Stars: 1754
 *   5 Stars: 39
 *   6 Stars: 1
 */

class Universe
{
    /**
     * @var array
     */
    static protected $weights = array(
        1 => 0.413019450,
        2 => 0.132378029,
        3 => 0.017650403,
        4 => 0.000968619,
        5 => 0.000018449,
        6 => 0.000000071,
    );

    /**
     * Randomly determine number of stars in a solar system.
     * Random number generation with a weight distribution.
     * Weights based on german lottery (% to win with X).
     *
     * @return integer The number of stars
     */
    static protected function getNumberOfStars()
    {
        $distribution = array();
        $total = 0;

        foreach (self::$weights as $key => $weight) {
            $total += $weight;
        }

        foreach (self::$weights as $key => $weight) {
            $distribution[$key] = $weight / $total;
        }

        $random = rand() / getrandmax();
        while (true) {
            foreach ($distribution as $key => $weight) {
                if (($random -= $weight) < 0) {
                    return $key;
                }
            }
        }
    }
}