From dc1539ae02fcb9c22b98d587b790ce8bc3a68774 Mon Sep 17 00:00:00 2001
From: Ben Pfaff <blp@nicira.com>
Date: Thu, 24 Mar 2011 09:40:07 -0700
Subject: [PATCH] list: New functions list_is_singleton(), list_is_short().

---
 lib/list.c        | 16 +++++++++++++++-
 lib/list.h        |  2 ++
 tests/test-list.c |  4 +++-
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/lib/list.c b/lib/list.c
index 0f4f2f84..b5fa3893 100644
--- a/lib/list.c
+++ b/lib/list.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009, 2010 Nicira Networks.
+ * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -168,3 +168,17 @@ list_is_empty(const struct list *list)
 {
     return list->next == list;
 }
+
+/* Returns true if 'list' has exactly 1 element, false otherwise. */
+bool
+list_is_singleton(const struct list *list)
+{
+    return list_is_short(list) && !list_is_empty(list);
+}
+
+/* Returns true if 'list' has 0 or 1 elements, false otherwise. */
+bool
+list_is_short(const struct list *list)
+{
+    return list->next == list->prev;
+}
diff --git a/lib/list.h b/lib/list.h
index 915ee854..91c39663 100644
--- a/lib/list.h
+++ b/lib/list.h
@@ -53,6 +53,8 @@ struct list *list_back(const struct list *);
 /* List properties. */
 size_t list_size(const struct list *);
 bool list_is_empty(const struct list *);
+bool list_is_singleton(const struct list *);
+bool list_is_short(const struct list *);
 
 #define LIST_FOR_EACH(ITER, MEMBER, LIST)                               \
     for (ASSIGN_CONTAINER(ITER, (LIST)->next, MEMBER);                  \
diff --git a/tests/test-list.c b/tests/test-list.c
index 5e62e0c0..b4ddd02e 100644
--- a/tests/test-list.c
+++ b/tests/test-list.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009, 2010 Nicira Networks.
+ * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -73,6 +73,8 @@ check_list(struct list *list, const int values[], size_t n)
     assert(i == n);
 
     assert(list_is_empty(list) == !n);
+    assert(list_is_singleton(list) == (n == 1));
+    assert(list_is_short(list) == (n < 2));
     assert(list_size(list) == n);
 }
 
-- 
2.30.2