From 8a5d001e29961de85426a22581aeec218a40e3d2 Mon Sep 17 00:00:00 2001
From: Pavel Kirienko <pavel.kirienko@gmail.com>
Date: Sun, 18 Jan 2015 01:20:56 +0300
Subject: [PATCH] Linked list: optimized insertBefore(), elaborated docs

---
 libuavcan/include/uavcan/util/linked_list.hpp | 17 +++++++++++++----
 libuavcan/test/util/linked_list.cpp           | 16 ++++++++++++++++
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/libuavcan/include/uavcan/util/linked_list.hpp b/libuavcan/include/uavcan/util/linked_list.hpp
index c907a28bb7..963cee9f02 100644
--- a/libuavcan/include/uavcan/util/linked_list.hpp
+++ b/libuavcan/include/uavcan/util/linked_list.hpp
@@ -57,19 +57,22 @@ public:
     unsigned getLength() const;
 
     /**
-     * Complexity: O(N) (calls remove())
+     * Inserts the node to the beginning of the list.
+     * If the node is already present in the list, it will be relocated to the beginning.
+     * Complexity: O(N)
      */
     void insert(T* node);
 
     /**
-     * Inserts the node immediately before the node B where
-     *  predicate(B) -> true.
+     * Inserts the node immediately before the node X where predicate(X) returns true.
+     * If the node is already present in the list, it can be relocated to a new position.
      * Complexity: O(2N) (calls remove())
      */
     template <typename Predicate>
     void insertBefore(T* node, Predicate predicate);
 
     /**
+     * Removes only the first occurence of the node.
      * Complexity: O(N)
      */
     void remove(const T* node);
@@ -107,11 +110,17 @@ template <typename Predicate>
 void LinkedListRoot<T>::insertBefore(T* node, Predicate predicate)
 {
     UAVCAN_ASSERT(node);
+    if (node == NULL)
+    {
+        return;
+    }
+
     remove(node);
 
     if (root_ == NULL || predicate(root_))
     {
-        insert(node);
+        node->setNextListNode(root_);
+        root_ = node;
     }
     else
     {
diff --git a/libuavcan/test/util/linked_list.cpp b/libuavcan/test/util/linked_list.cpp
index 392215a934..96c8be0e6d 100644
--- a/libuavcan/test/util/linked_list.cpp
+++ b/libuavcan/test/util/linked_list.cpp
@@ -104,11 +104,27 @@ TEST(LinkedList, Sorting)
     uavcan::LinkedListRoot<ListItem> root;
     ListItem items[] = {0, 1, 2, 3, 4, 5};
 
+    EXPECT_EQ(0, root.getLength());
+
     items[2].insort(root);
+    EXPECT_EQ(1, root.getLength());
+
+    items[2].insort(root);              // Making sure the duplicate will be removed
+    EXPECT_EQ(1, root.getLength());
+
     items[3].insort(root);
+
     items[0].insort(root);
+
     items[4].insort(root);
+    EXPECT_EQ(4, root.getLength());
+
     items[1].insort(root);
+    EXPECT_EQ(5, root.getLength());
+
+    items[1].insort(root);              // Another duplicate
+    EXPECT_EQ(5, root.getLength());
+
     items[5].insort(root);
 
     EXPECT_EQ(6, root.getLength());