Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.289
diff -u -p -r1.289 bootstrap.inc
--- includes/bootstrap.inc	14 Jul 2009 10:22:15 -0000	1.289
+++ includes/bootstrap.inc	18 Jul 2009 19:54:35 -0000
@@ -1024,11 +1024,21 @@ function drupal_unpack($obj, $field = 'd
 /**
  * Encode special characters in a plain-text string for display as HTML.
  *
- * Uses drupal_validate_utf8 to prevent cross site scripting attacks on
- * Internet Explorer 6.
+ * check_plain() also validates strings as UTF-8 to prevent cross site scripting
+ * attacks on Internet Explorer 6. We duplicate the preg_match() from
+ * drupal_validate_utf8() here rather than calling the function to avoid
+ * the overhead of an additional function call, since check_plain() may be
+ * called hundreds of times during a request.
+ *
+ * @param $text
+ *   The text to be checked or processed.
+ * @return
+ *   An HTML safe version of $text, or an empty string if $text is not
+ *   valid UTF-8.
+ * @see drupal_validate_utf8().
  */
 function check_plain($text) {
-  return drupal_validate_utf8($text) ? htmlspecialchars($text, ENT_QUOTES) : '';
+  return (preg_match('/^./us', $text) == 1) ? htmlspecialchars($text, ENT_QUOTES) : '';
 }
 
 /**