+ Apart from the type `struct name' and the definition of SUCCESSOR,
+ this is a generic list-sorting function, but it's too painful to
+ make it both generic and portable
+ in C. */
+
+static struct name *
+merge_sort_sll (struct name *list, int length,
+ int (*compare) (struct name const*, struct name const*))
+{
+ struct name *first_list;
+ struct name *second_list;
+ int first_length;
+ int second_length;
+ struct name *result;
+ struct name **merge_point;
+ struct name *cursor;
+ int counter;
+
+# define SUCCESSOR(name) ((name)->next)
+
+ if (length == 1)
+ return list;
+
+ if (length == 2)
+ {
+ if ((*compare) (list, SUCCESSOR (list)) > 0)
+ {
+ result = SUCCESSOR (list);
+ SUCCESSOR (result) = list;
+ SUCCESSOR (list) = 0;
+ return result;
+ }
+ return list;
+ }
+
+ first_list = list;
+ first_length = (length + 1) / 2;
+ second_length = length / 2;
+ for (cursor = list, counter = first_length - 1;
+ counter;
+ cursor = SUCCESSOR (cursor), counter--)
+ continue;
+ second_list = SUCCESSOR (cursor);
+ SUCCESSOR (cursor) = 0;
+
+ first_list = merge_sort_sll (first_list, first_length, compare);
+ second_list = merge_sort_sll (second_list, second_length, compare);
+
+ merge_point = &result;
+ while (first_list && second_list)
+ if ((*compare) (first_list, second_list) < 0)
+ {
+ cursor = SUCCESSOR (first_list);
+ *merge_point = first_list;
+ merge_point = &SUCCESSOR (first_list);
+ first_list = cursor;
+ }
+ else
+ {
+ cursor = SUCCESSOR (second_list);
+ *merge_point = second_list;
+ merge_point = &SUCCESSOR (second_list);
+ second_list = cursor;
+ }
+ if (first_list)
+ *merge_point = first_list;
+ else
+ *merge_point = second_list;
+
+ return result;
+
+#undef SUCCESSOR
+}
+
+/* Sort doubly linked LIST of names, of given LENGTH, using COMPARE
+ to order names. Return the sorted list. */
+static struct name *
+merge_sort (struct name *list, int length,
+ int (*compare) (struct name const*, struct name const*))