ldb: sync DLIST_DEMOTE_SHORT() changes to include/dlinklist.h

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>

lib/ldb/include/dlinklist.h

@@ -156,6 +156,27 @@ do { \
 	DLIST_ADD_END(list, p); \
 } while (0)
 
+/*
+ * like DLIST_DEMOTE(), but optimized
+ * for short lists with 0, 1 or 2 elements
+ */
+#define DLIST_DEMOTE_SHORT(list, p) \
+do { \
+	if ((list) == NULL) { \
+		/* no reason to demote, just add */ \
+		DLIST_ADD(list, p); \
+	} else if ((list)->prev == (p)) { \
+		/* optimize if p is last */ \
+	} else if ((list) == (p)) { \
+		/* optimize if p is first */ \
+		(list)->prev->next = (p); \
+		(list) = (p)->next; \
+		(p)->next = NULL; \
+	} else { \
+		DLIST_DEMOTE(list, p); \
+	} \
+} while (0)
+
 /*
    concatenate two lists - putting all elements of the 2nd list at the
    end of the first list.