From cbca8de5884ff62614e78076dffc093e8373e492 Mon Sep 17 00:00:00 2001
From: mdkinney <mdkinney@6f19259b-4bc3-4df7-8a09-765794883524>
Date: Sat, 21 Nov 2009 21:57:11 +0000
Subject: 1) Add new BaseLib API GetPreviousNode() 2) Clarify comment for the
 value returned from GetNextNode() if the end of list is reached.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@9464 6f19259b-4bc3-4df7-8a09-765794883524
---
 MdePkg/Library/BaseLib/LinkedList.c | 39 +++++++++++++++++++++++++++++++++++--
 1 file changed, 37 insertions(+), 2 deletions(-)

(limited to 'MdePkg/Library/BaseLib')

diff --git a/MdePkg/Library/BaseLib/LinkedList.c b/MdePkg/Library/BaseLib/LinkedList.c
index 3ff582a978..0c811b0bff 100644
--- a/MdePkg/Library/BaseLib/LinkedList.c
+++ b/MdePkg/Library/BaseLib/LinkedList.c
@@ -276,8 +276,7 @@ GetFirstNode (
   @param  List  A pointer to the head node of a doubly linked list.
   @param  Node  A pointer to a node in the doubly linked list.
 
-  @return Pointer to the next node if one exists. Otherwise a null value which
-          is actually List is returned.
+  @return Pointer to the next node if one exists. Otherwise List is returned.
 
 **/
 LIST_ENTRY *
@@ -295,6 +294,42 @@ GetNextNode (
   return Node->ForwardLink;
 }
 
+/**
+  Retrieves the previous node of a doubly linked list.
+ 
+  Returns the node of a doubly linked list that precedes Node.  
+  List must have been initialized with INTIALIZE_LIST_HEAD_VARIABLE()
+  or InitializeListHead().  If List is empty, then List is returned.
+ 
+  If List is NULL, then ASSERT().
+  If Node is NULL, then ASSERT().
+  If List was not initialized with INTIALIZE_LIST_HEAD_VARIABLE() or 
+  InitializeListHead(), then ASSERT().
+  If PcdMaximumLinkedListLenth is not zero, and List contains more than
+  PcdMaximumLinkedListLenth nodes, then ASSERT().
+  If PcdVerifyNodeInList is TRUE and Node is not a node in List, then ASSERT().
+ 
+  @param  List  A pointer to the head node of a doubly linked list.
+  @param  Node  A pointer to a node in the doubly linked list.
+ 
+  @return Pointer to the previous node if one exists. Otherwise List is returned.
+ 
+**/
+LIST_ENTRY *
+EFIAPI
+GetPreviousNode (
+  IN      CONST LIST_ENTRY          *List,
+  IN      CONST LIST_ENTRY          *Node
+  )
+{
+  //
+  // ASSERT List not too long and Node is one of the nodes of List
+  //
+  ASSERT (InternalBaseLibIsNodeInList (List, Node, TRUE));
+ 
+  return Node->BackLink;
+}
+
 /**
   Checks to see if a doubly linked list is empty or not.
 
-- 
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