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+------------------------------------------------------------------------------
+-- --
+-- GNAT LIBRARY COMPONENTS --
+-- --
+-- ADA.CONTAINERS.UNBOUNDED_PRIORITY_QUEUES --
+-- --
+-- B o d y --
+-- --
+-- Copyright (C) 2011, Free Software Foundation, Inc. --
+-- --
+-- GNAT is free software; you can redistribute it and/or modify it under --
+-- terms of the GNU General Public License as published by the Free Soft- --
+-- ware Foundation; either version 3, or (at your option) any later ver- --
+-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
+-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
+-- or FITNESS FOR A PARTICULAR PURPOSE. --
+-- --
+-- As a special exception under Section 7 of GPL version 3, you are granted --
+-- additional permissions described in the GCC Runtime Library Exception, --
+-- version 3.1, as published by the Free Software Foundation. --
+-- --
+-- You should have received a copy of the GNU General Public License and --
+-- a copy of the GCC Runtime Library Exception along with this program; --
+-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
+-- <http://www.gnu.org/licenses/>. --
+-- --
+-- This unit was originally developed by Matthew J Heaney. --
+------------------------------------------------------------------------------
+
+with Ada.Unchecked_Deallocation;
+
+package body Ada.Containers.Unbounded_Priority_Queues is
+
+ package body Implementation is
+
+ -----------------------
+ -- Local Subprograms --
+ -----------------------
+
+ procedure Free is
+ new Ada.Unchecked_Deallocation (Node_Type, Node_Access);
+
+ -------------
+ -- Dequeue --
+ -------------
+
+ procedure Dequeue
+ (List : in out List_Type;
+ Element : out Queue_Interfaces.Element_Type)
+ is
+ X : Node_Access;
+
+ begin
+ Element := List.First.Element;
+
+ X := List.First;
+ List.First := List.First.Next;
+
+ if List.First = null then
+ List.Last := null;
+ end if;
+
+ List.Length := List.Length - 1;
+
+ Free (X);
+ end Dequeue;
+
+ procedure Dequeue
+ (List : in out List_Type;
+ At_Least : Queue_Priority;
+ Element : in out Queue_Interfaces.Element_Type;
+ Success : out Boolean)
+ is
+ begin
+ -- This operation dequeues a high priority item if it exists in the
+ -- queue. By "high priority" we mean an item whose priority is equal
+ -- or greater than the value At_Least. The generic formal operation
+ -- Before has the meaning "has higher priority than". To dequeue an
+ -- item (meaning that we return True as our Success value), we need
+ -- as our predicate the equivalent of "has equal or higher priority
+ -- than", but we cannot say that directly, so we require some logical
+ -- gymnastics to make it so.
+
+ -- If E is the element at the head of the queue, and symbol ">"
+ -- refers to the "is higher priority than" function Before, then we
+ -- derive our predicate as follows:
+ -- original: P(E) >= At_Least
+ -- same as: not (P(E) < At_Least)
+ -- same as: not (At_Least > P(E))
+ -- same as: not Before (At_Least, P(E))
+
+ -- But that predicate needs to be true in order to successfully
+ -- dequeue an item. If it's false, it means no item is dequeued, and
+ -- we return False as the Success value.
+
+ if List.Length = 0
+ or else Before (At_Least, Get_Priority (List.First.Element))
+ then
+ Success := False;
+ return;
+ end if;
+
+ List.Dequeue (Element);
+ Success := True;
+ end Dequeue;
+
+ -------------
+ -- Enqueue --
+ -------------
+
+ procedure Enqueue
+ (List : in out List_Type;
+ New_Item : Queue_Interfaces.Element_Type)
+ is
+ P : constant Queue_Priority := Get_Priority (New_Item);
+
+ Node : Node_Access;
+ Prev : Node_Access;
+
+ begin
+ Node := new Node_Type'(New_Item, null);
+
+ if List.First = null then
+ List.First := Node;
+ List.Last := List.First;
+
+ else
+ Prev := List.First;
+
+ if Before (P, Get_Priority (Prev.Element)) then
+ Node.Next := List.First;
+ List.First := Node;
+
+ else
+ while Prev.Next /= null loop
+ if Before (P, Get_Priority (Prev.Next.Element)) then
+ Node.Next := Prev.Next;
+ Prev.Next := Node;
+
+ exit;
+ end if;
+
+ Prev := Prev.Next;
+ end loop;
+
+ if Prev.Next = null then
+ List.Last.Next := Node;
+ List.Last := Node;
+ end if;
+ end if;
+ end if;
+
+ List.Length := List.Length + 1;
+
+ if List.Length > List.Max_Length then
+ List.Max_Length := List.Length;
+ end if;
+ end Enqueue;
+
+ --------------
+ -- Finalize --
+ --------------
+
+ procedure Finalize (List : in out List_Type) is
+ X : Node_Access;
+ begin
+ while List.First /= null loop
+ X := List.First;
+ List.First := List.First.Next;
+ Free (X);
+ end loop;
+ end Finalize;
+
+ ------------
+ -- Length --
+ ------------
+
+ function Length (List : List_Type) return Count_Type is
+ begin
+ return List.Length;
+ end Length;
+
+ ----------------
+ -- Max_Length --
+ ----------------
+
+ function Max_Length (List : List_Type) return Count_Type is
+ begin
+ return List.Max_Length;
+ end Max_Length;
+
+ end Implementation;
+
+ protected body Queue is
+
+ -----------------
+ -- Current_Use --
+ -----------------
+
+ function Current_Use return Count_Type is
+ begin
+ return List.Length;
+ end Current_Use;
+
+ -------------
+ -- Dequeue --
+ -------------
+
+ entry Dequeue (Element : out Queue_Interfaces.Element_Type)
+ when List.Length > 0
+ is
+ begin
+ List.Dequeue (Element);
+ end Dequeue;
+
+ --------------------------------
+ -- Dequeue_Only_High_Priority --
+ --------------------------------
+
+ procedure Dequeue_Only_High_Priority
+ (At_Least : Queue_Priority;
+ Element : in out Queue_Interfaces.Element_Type;
+ Success : out Boolean)
+ is
+ begin
+ List.Dequeue (At_Least, Element, Success);
+ end Dequeue_Only_High_Priority;
+
+ -------------
+ -- Enqueue --
+ -------------
+
+ entry Enqueue (New_Item : Queue_Interfaces.Element_Type) when True is
+ begin
+ List.Enqueue (New_Item);
+ end Enqueue;
+
+ --------------
+ -- Peak_Use --
+ --------------
+
+ function Peak_Use return Count_Type is
+ begin
+ return List.Max_Length;
+ end Peak_Use;
+
+ end Queue;
+
+end Ada.Containers.Unbounded_Priority_Queues;