X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Flib%2Fkernel%2Flist.c;h=ba4fae68bfe51919dc30a43007f634c2fa8d0474;hb=0ec49949304b13ff22287d7d9e3dcb05090c61a4;hp=3631b2e68da0ddc5292c588bf0acbe34fb1ca996;hpb=f2f8875638593bd5365cfd6a5ba7c9578e52322f;p=pintos-anon

diff --git a/src/lib/kernel/list.c b/src/lib/kernel/list.c
index 3631b2e..ba4fae6 100644
--- a/src/lib/kernel/list.c
+++ b/src/lib/kernel/list.c
@@ -78,7 +78,7 @@ list_begin (struct list *list)
 list_elem *
 list_next (list_elem *elem)
 {
-  ASSERT (is_interior (elem));
+  ASSERT (is_head (elem) || is_interior (elem));
   return elem->next;
 }
 
@@ -216,15 +216,15 @@ list_push_back (struct list *list, list_elem *elem)
   list_insert (list_end (list), elem);
 }
 
-/* Removes ELEM from its list.  Undefined behavior if ELEM is not
-   in a list. */
+/* Removes ELEM from its list and returns the element that
+   followed it.  Undefined behavior if ELEM is not in a list.  */
 list_elem *
 list_remove (list_elem *elem)
 {
   ASSERT (is_interior (elem));
   elem->prev->next = elem->next;
   elem->next->prev = elem->prev;
-  return elem;
+  return elem->next;
 }
 
 /* Removes the front element from LIST and returns it.
@@ -232,8 +232,9 @@ list_remove (list_elem *elem)
 list_elem *
 list_pop_front (struct list *list)
 {
-  ASSERT (list != NULL);
-  return list_remove (list_front (list));
+  list_elem *front = list_front (list);
+  list_remove (front);
+  return front;
 }
 
 /* Removes the back element from LIST and returns it.
@@ -241,8 +242,9 @@ list_pop_front (struct list *list)
 list_elem *
 list_pop_back (struct list *list)
 {
-  ASSERT (list != NULL);
-  return list_remove (list_back (list));
+  list_elem *back = list_back (list);
+  list_remove (back);
+  return back;
 }
 
 /* Returns the front element in LIST.
@@ -283,24 +285,28 @@ list_empty (struct list *list)
   return list_begin (list) == list_end (list);
 }
 
+/* Swaps the `list_elem *'s that A and B point to. */
+static void
+swap (list_elem **a, list_elem **b) 
+{
+  list_elem *t = *a;
+  *a = *b;
+  *b = t;
+}
+
 /* Reverses the order of LIST. */
 void
 list_reverse (struct list *list)
 {
-  list_elem te, *e;
-
-  /* Swap the prev and next pointers in each element of LIST. */
-  for (e = &list->head; e != NULL; e = e->prev)
+  if (!list_empty (list)) 
     {
-      list_elem *tep = e->prev;
-      e->prev = e->next;
-      e->next = tep;
-    }
+      list_elem *e;
 
-  /* Swap the head and tail. */
-  te = list->head;
-  list->head = list->tail;
-  list->tail = te;
+      for (e = list_begin (list); e != list_end (list); e = e->prev)
+        swap (&e->prev, &e->next);
+      swap (&list->head.next, &list->tail.prev);
+      swap (&list->head.next->prev, &list->tail.prev->next);
+    }
 }
 
 /* Merges lists AL and BL, which must each be sorted according to
@@ -351,8 +357,7 @@ list_sort (struct list *list,
 
   /* Find middle of LIST.  (We're not interested in the end of
      the list but it's incidentally needed.) */
-  middle = list_begin (list);
-  last = list_next (middle);
+  middle = last = list_begin (list);
   while (last != list_end (list) && list_next (last) != list_end (list))
     {
       middle = list_next (middle);