From 031cf17e974a9ea972bd5ae22272f9f089527b78 Mon Sep 17 00:00:00 2001
From: Ben Pfaff <blp@cs.stanford.edu>
Date: Fri, 3 Sep 2004 06:25:36 +0000
Subject: [PATCH] Add list_head(), list_tail().

---
 src/lib/list.c | 38 ++++++++++++++++++++++++++++++++------
 src/lib/list.h | 11 +++++++----
 2 files changed, 39 insertions(+), 10 deletions(-)

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
diff --git a/src/lib/list.h b/src/lib/list.h
index a808606..1bf6631 100644
--- a/src/lib/list.h
+++ b/src/lib/list.h
@@ -89,16 +89,16 @@
 /* List element. */
 typedef struct list_elem 
   {
-    struct list_elem *prev; /* Previous node in list. */
-    struct list_elem *next; /* Next node in list. */
+    struct list_elem *prev;     /* Previous list element. */
+    struct list_elem *next;     /* Next list element. */
   }
 list_elem;
 
 /* List. */
 struct list 
   {
-    list_elem head; /* Start-of-list header node. */
-    list_elem tail; /* End-of-list header node. */
+    list_elem head;             /* List head. */
+    list_elem tail;             /* List tail. */
   };
 
 /* Converts pointer to list element LIST_ELEM into a pointer to
@@ -120,6 +120,9 @@ list_elem *list_rbegin (struct list *);
 list_elem *list_prev (list_elem *);
 list_elem *list_rend (struct list *);
 
+list_elem *list_head (struct list *);
+list_elem *list_tail (struct list *);
+
 /* List insertion. */
 void list_insert (list_elem *, list_elem *);
 void list_splice (list_elem *before,
-- 
2.30.2