X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Flib%2Flist.c;h=a5f7c1a6c573fb638d2fadcff8a2d034bd51c7f7;hb=dca7bfbc436c5305ef8f0df6fbe1faba89a0012e;hp=0011fc7e5793f72a9855455af7db6c5734927127;hpb=8051f62ca0af42761608b8917e7524aaabc6cdcf;p=pintos-anon

diff --git a/src/lib/list.c b/src/lib/list.c
index 0011fc7..a5f7c1a 100644
--- a/src/lib/list.c
+++ b/src/lib/list.c
@@ -103,6 +103,16 @@ list_rbegin (struct list *list)
   return list->tail.prev;
 }
 
+/* Returns the element before ELEM in its list.  If ELEM is the
+   first element in its list, returns the list head.  Results are
+   undefined if ELEM is itself a list head. */
+list_elem *
+list_prev (list_elem *elem)
+{
+  ASSERT (is_interior (elem) || is_tail (elem));
+  return elem->prev;
+}
+
 /* Returns LIST's head.
 
    list_rend() is often used in iterating through a list in
@@ -123,14 +133,30 @@ list_rend (struct list *list)
   return &list->head;
 }
 
-/* Returns the element before ELEM in its list.  If ELEM is the
-   first element in its list, returns the list head.  Results are
-   undefined if ELEM is itself a list head. */
+/* Return's LIST's head.
+
+   list_head() can be used for an alternate style of iterating
+   through a list, e.g.:
+
+      e = list_head (&list);
+      while ((e = list_next (e)) != list_end (&list)) 
+        {
+          ...
+        }
+*/
 list_elem *
-list_prev (list_elem *elem)
+list_head (struct list *list) 
 {
-  ASSERT (is_interior (elem) || is_tail (elem));
-  return elem->prev;
+  ASSERT (list != NULL);
+  return &list->head;
+}
+
+/* Return's LIST's tail. */
+list_elem *
+list_tail (struct list *list) 
+{
+  ASSERT (list != NULL);
+  return &list->tail;
 }
 
 /* Inserts ELEM just before BEFORE, which may be either an