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------------------------------------------------------------------------------ -- -- -- GNAT LIBRARY COMPONENTS -- -- -- -- ADA.CONTAINERS.BOUNDED_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. -- ------------------------------------------------------------------------------ package body Ada.Containers.Bounded_Priority_Queues is package body Implementation is ------------- -- Dequeue -- ------------- procedure Dequeue (List : in out List_Type; Element : out Queue_Interfaces.Element_Type) is begin Element := List.Container.First_Element; List.Container.Delete_First; 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.Container.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); C : List_Types.Cursor; use List_Types; Count : Count_Type; begin C := List.Container.First; while Has_Element (C) loop -- ??? why is following commented out ??? -- if Before (P, Get_Priority (List.Constant_Reference (C))) then if Before (P, Get_Priority (Element (C))) then List.Container.Insert (C, New_Item); exit; end if; Next (C); end loop; if not Has_Element (C) then List.Container.Append (New_Item); end if; Count := List.Container.Length; if Count > List.Max_Length then List.Max_Length := Count; end if; end Enqueue; ------------------- -- First_Element -- ------------------- function First_Element (List : List_Type) return Queue_Interfaces.Element_Type is begin -- Use Constant_Reference for this. ??? return List.Container.First_Element; end First_Element; ------------ -- Length -- ------------ function Length (List : List_Type) return Count_Type is begin return List.Container.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 List.Length < Capacity 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.Bounded_Priority_Queues;
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