1 files changed, 72 insertions, 0 deletions
diff --git a/src/backend/lib/dllist.h b/src/backend/lib/dllist.h
new file mode 100644
index 00000000000..cd9ac42a12f
--- /dev/null
+++ b/src/backend/lib/dllist.h
@@ -0,0 +1,72 @@
+/*-------------------------------------------------------------------------
+ *
+ * dllist.h--
+ *      simple doubly linked list primitives
+ *      the elements of the list are void* so the lists can contain
+ *      anything
+ *      Dlelem can only be in one list at a time
+ *     
+ *
+ *   Here's a small example of how to use Dllist's :
+ * 
+ *   Dllist *lst;
+ *   Dlelem *elt;
+ *   void   *in_stuff;    -- stuff to stick in the list
+ *   void   *out_stuff
+ *
+ *   lst = DLNewList();                -- make a new dllist
+ *   DLAddHead(lst, DLNewElem(in_stuff)); -- add a new element to the list
+ *                                           with in_stuff as the value
+ *    ...  
+ *   elt = DLGetHead(lst);             -- retrieve the head element
+ *   out_stuff = (void*)DLE_VAL(elt);  -- get the stuff out
+ *   DLRemove(elt);                    -- removes the element from its list
+ *   DLFreeElem(elt);                  -- free the element since we don't
+ *                                        use it anymore
+ *
+ * Copyright (c) 1994, Regents of the University of California
+ *
+ * $Id: dllist.h,v 1.1.1.1 1996/07/09 06:21:28 scrappy Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef DLLIST_H
+#define DLLIST_H
+
+#include "c.h"
+
+struct Dllist;
+struct Dlelem;
+
+typedef struct Dlelem {
+  struct Dlelem *dle_next;  /* next element */
+  struct Dlelem *dle_prev;  /* previous element */
+  void   *dle_val; /* value of the element */
+  struct Dllist *dle_list;  /* what list this element is in */
+} Dlelem;
+
+typedef struct Dllist {
+  Dlelem *dll_head;
+  Dlelem *dll_tail;
+} Dllist;
+  
+extern Dllist* DLNewList(); /* initialize a new list */
+extern void    DLFreeList(Dllist*); /* free up a list and all the nodes in it*/
+extern Dlelem* DLNewElem(void* val); 
+extern void    DLFreeElem(Dlelem*); 
+extern Dlelem* DLGetHead(Dllist*);
+extern Dlelem* DLGetTail(Dllist*);
+extern void*   DLGetHeadVal(Dllist*);
+extern void*   DLGetTailVal(Dllist*);
+extern Dlelem* DLGetPred(Dlelem*); /* get predecessor */
+extern Dlelem* DLGetSucc(Dlelem*); /* get successor */
+extern void    DLRemove(Dlelem*); /* removes node from list*/
+extern void    DLAddHead(Dllist* list, Dlelem* node);
+extern void    DLAddTail(Dllist* list, Dlelem* node);
+extern Dlelem* DLRemHead(Dllist* list); /* remove and return the head */
+extern Dlelem* DLRemTail(Dllist* list); /* remove and return the tail */
+
+#define DLE_VAL(x)  (x->dle_val)
+
+#endif /* DLLIST_H */