course sorting MDL-21011 "Re-sort courses by name" button eventually lead sortorder to hit column maximum value

course/category.php

@@ -57,9 +57,9 @@
         if ($resort and confirm_sesskey()) {
             if ($courses = get_courses($category->id, "fullname ASC", 'c.id,c.fullname,c.sortorder')) {
                 // move it off the range
-                $count = get_record_sql('SELECT MAX(sortorder) AS max, 1
+                $count = get_record_sql('SELECT MIN(sortorder) AS min, 1
                                          FROM ' . $CFG->prefix . 'course WHERE category=' . $category->id);
-                $count = $count->max + 100;
+                $count = $count->min;
                 begin_sql();
                 foreach ($courses as $course) {
                     set_field('course', 'sortorder', $count, 'id', $course->id);

lib/datalib.php

@@ -1343,7 +1343,7 @@ function fix_course_sortorder($categoryid=0, $n=0, $safe=0, $depth=0, $path='')
     // $mustshift indicates whether the sequence must be shifted to
     // meet its range
     $mustshift = false;
-    if ($min < $n+$tolerance || $min > $n+$tolerance+$catgap ) {
+    if ($min < $n-$tolerance || $min > $n+$tolerance+$catgap ) {
         $mustshift = true;
     }