From: Martin Mares <mj@ucw.cz>
Date: Mon, 15 Jan 2001 09:24:16 +0000 (+0000)
Subject: Added an explanatory comment.
X-Git-Tag: v1.2.0~477
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a2d01907c5b24bab78cc055fa23354597bd44a03;p=thirdparty%2Fbird.git

Added an explanatory comment.
---

diff --git a/lib/lists.h b/lib/lists.h
index acab292e9..5b36ec83e 100644
--- a/lib/lists.h
+++ b/lib/lists.h
@@ -9,6 +9,19 @@
 #ifndef _BIRD_LISTS_H_
 #define _BIRD_LISTS_H_
 
+/*
+ * I admit the list structure is very tricky and also somewhat awkward,
+ * but it's both efficient and easy to manipulate once one understands the
+ * basic trick: The list head always contains two synthetic nodes which are
+ * always present in the list: the head and the tail. But as the `next'
+ * entry of the tail and the `prev' entry of the head are both NULL, the
+ * nodes can overlap each other:
+ *
+ *     head    head_node.next
+ *     null    head_node.prev  tail_node.next
+ *     tail                    tail_node.prev
+ */
+
 typedef struct node {
   struct node *next, *prev;
 } node;