Get index of FEN string for given blocks

gistfile1.php

<?php

/** function get_index
 *
 *	Gets the FEN string index for a 2D location
 *	of a square array of blocks each containing
 *	a square array of elements within those blocks
 *
 *	This was designed for use within foreach structures
 *	The first foreach ($i) is the outer blocks, and the 
 *	second ($j)	is for the inner elements.
 *
 *	Example Structure:
 *		+----+----+----++----+----+----+
 *		|  0 |  1 |  2 ||  3 |  4 |  5 |
 *		+----+----+----++----+----+----+
 *		|  6 |  7 |  8 ||  9 | 10 | 11 |
 *		+----+----+----++----+----+----+
 *		| 12 | 13 | 14 || 15 | 16 | 17 |
 *		+====+====+====++====+====+====+
 *		| 18 | 19 | 20 || 21 | 22 | 23 |
 *		+----+----+----++----+----+----+
 *		| 24 | 25 | 26 || 27 | 28 | 29 |
 *		+----+----+----++----+----+----+
 *		| 30 | 31 | 32 || 33 | 34 | 35 |
 *		+----+----+----++----+----+----+
 *
 *	Where $i = 2 (bottom left big block)
 *	  and $j = 5 (center element)
 *	 $blocks = 2 (number of blocks per side)
 *	  $elems = 3 (numer of elements per side in each block)
 *	will return 25 (the index of the string)
 *
 * @param int the current block number
 * @param int the current element number
 * @param int the number of blocks per side
 * @param int the number of elements per side
 * @return int the FEN string index
 */
function get_index($i, $j, $blocks = 3, $elems = 3) {
	$bits = array(
		($j % $elems), // across within block (across elems)
		((int) floor($j / $elems) * $blocks * $elems), // down within block (down elems)
		(($i % $blocks) * $elems), // across blocks
		((int) floor($i / $blocks) * $blocks * $elems * $elems), // down blocks
	);

	return array_sum($bits);
}