Merge pull request zendframework/zendframework#5815 in master

src/Object/Code128.php

@@ -208,7 +208,8 @@ protected function convertToBarcodeChars($string)
         $currentCharset = null;
         $result = array();
 
-        for ($pos = 0; $pos < strlen($string); $pos++) {
+        $strlen = strlen($string);
+        for ($pos = 0; $pos < $strlen; $pos++) {
             $char = $string[$pos];
             $code = null;