Binary GCD algorithm php implementation. Iterative version.

binaryGCDiterative.php

function binary_gcd($a, $b){
	/* computes and returns the greatest common divisor between a and b */
	
	/*
	 *	Binary GCD Algorithm, according to Wikipedia "binary GCD can be about 60% 
	 *	more efficient (in terms of the number of bit operations) on average than the Euclidean algorithm".

	 *	More about the Binary GCD Algorithm: http://en.wikipedia.org/wiki/Binary_GCD_algorithm
	 *	Java Implementation: http://introcs.cs.princeton.edu/java/23recursion/BinaryGCD.java.html
	 *  C++ Implementation: https://gist.github.com/cslarsen/1635213
	 */
	$shiftleft = 0;

	while( ($a && $b) && ($a != $b) ){
		$a_is_even = !($a & 1); // check if a is even
		$b_is_even = !($b & 1); // check if b is even

		// if both a and b are even
		if ($a_is_even && $b_is_even){
			$shiftleft++;
			$a >>= 1; // shift a right by 1 bit (i.e. divide by 2)
			$b >>= 1; // shift b right by 1 bit (i.e. divide by 2)
		}
		// if a is even and b is odd
		else if ($a_is_even && !$b_is_even)
			$a >>= 1;

		// if b is even and a is odd
		else if (!$a_is_even && $b_is_even)
			$b >>= 1;

		// if both a and b are odd and a >= b
		else if ($a >= $b)
			$a = ($a-$b) >> 1;

		// if both a and b are odd and a < b
		else{
			$temp = $a;
			$a = ($b - $a) >> 1;
			$b = $temp;
		}
	}

	// if $a is 0, then shift $b left by $shiftleft bits, otherwise, shit $a by $shiftleft bits
	return !$a ? $b << $shiftleft : $a << $shiftleft;

	/*
	 *	NOTE: Doing (inetger & 1) check if it's even.
	 *		  Example: 1 --> 0001
	 *		  		   6 --> 0110
	 *		  		   0001 & 0110 ---> 0000 (which is 0)
	 *
	 *		  		   1 --> 0001
	 *		  		   7 --> 0111
	 *		  		   0001 & 0111 ---> 0001 (which is 1)
	*/
}