Class for calculating the greatest common factor of two or more numbers.

class.php

<?php
/**
 * Greatest Common Factor.
 *
 * @package GreatestCommonFactor
 * @author  Gary Jones
 * @link    http://code.garyjones.co.uk/greatest-common-factor-class/
 * @license http://gamajo.mit-license.org/2011
 */

/**
 * GreatestCommonFactor is a class for finding the greatest common factor of two
 * or more numbers.
 *
 * Bit hat tip to http://www.calculatorsoup.com/calculators/math/gcf.php for the
 * initial logic.
 *
 * @package GreatestCommonFactor
 * @author  Gary Jones
 * @license http://gamajo.mit-license.org/2011
 */
class GreatestCommonFactor
{
    /**
	 * Holds all values.
	 *
	 * @var array
	 */
	protected $values = array();

	/**
	 * Grab values into array.
	 *
	 * @param int|array $arg Accepts either an array of integers, or
	 *                           multiple integer arguments
	 */
	public function __construct($arg)
	{
		if (func_num_args() > 1) {
			$this->values = func_get_args();
		} else {
			$this->values = (array) $arg;
		}
	}

	/**
	 * Add an extra value to the collection.
	 *
	 * @param int $value
	 */
	public function add($value) {
		array_push($this->values, $value);
	}

	/**
	 * Do the calculation of the GCF.
	 *
	 * @return int
	 */
	public function calculate()
	{
		$this->validate();

		// Count the number of values in the array
		$num_values = count($this->values);

		// Get the first 2 values in the array
		$x = current($this->values);
		$y = next($this->values);

		// set up a for-loop to check through all of the values in the array
		// the first pass will check two numbers then each additional pass will
		// check one more, giving ($num_values - 1) passes
		for ($i = 1; $i < $num_values; $i++) {
			// Set up the larger and smaller of the values
			$a = max($x, $y);
			$b = min($x, $y);
			$c = 1;

			// Find the greatest common factor of $a and $b
			// It will be found when $c == 0
			do {
				$c = $a % $b;

				// Capture last value of $b as the potential last GCF result
				$gcf = $b;

				// If $c did not equal 0 we need to repeat with the values held
				// in $b and $c. At this point $b is higher than $c so we set up
				// for the next iteration, setting $a to the higher number and
				// $b to the lower number
				$a = $b;
				$b = $c;
			} while ($c != 0);

			// If $c == 0 then we have found the GCF of 2 numbers
			// now set up to find the GCF of the last GCF we found and the next value in the array()
			$x = $gcf;
			$y = next($this->values);
		}

		return $gcf;
	}

	/**
	 * Check that the values to calculate the result from are all valid.
	 *
	 * @throws BadMethodCallException
	 * @throws InvalidArgumentException
	 */
	protected function validate() {
		// Check we have at least two values
		if (count($this->values) < 2) {
			throw new BadMethodCallException('Not enough values submitted to find the greatest common factor.');
		}

		// Loop through each value to check it is valid
		foreach ($this->values as $value) {
			if (is_int($value) && $value > 0) {
				throw new InvalidArgumentException('The value of ' . $value . ' is invalid for finding the greatest common factor.');
			}
		}
	}
}

usage.php

<?php

// Use an array
$values = array(225, 45, 15, 540); // Maybe pulled from external source
$gcf = new GreatestCommonFactor($values);
echo 'GCF = ' . $gcf->calculate();
// Outputs: GCF = 15

// Use a comma-separated list of numbers
$gcf = new GreatestCommonFactor(225, 45, 15, 540);
echo 'GCF = ' . $gcf->calculate();
// Outputs: GCF = 15