Simple PHP entropy calculator

entropizer.php

<?php
/**
 * Calculate entropy of a string
 *
 * @see    https://github.com/jreesuk/entropizer
 *
 * @param  string $str
 * @return integer
 */
function entropizer($str) {
	$classes = array(
		array("regex" => "/[a-z]/", "size" => 26),
		array("regex" => "/[A-Z]/", "size" => 26),
		array("regex" => "/[0-9]/", "size" => 10),
		" ,.?!\"£$%^&*()-_=+[]{};:\'@#~<>/\\|`¬¦"
	);
	$size = 0;
	$str = trim($str);
	foreach($classes as $case) {
		if(is_array($case)) {
			if(preg_match($case["regex"], $str)) {
				$size += $case["size"];
			}
		} else {
			foreach(str_split($case, 1) as $char) {
				if(strpos($str, $char) !== false) {
					$size += strlen($case);
					break;
				}
			}
		}
	}
	return floor(log($size, 2) * strlen($str));
}