Yurttas/PL/IL/Ada-95/F/03/02/01/queue 02 p.adb

 1--
 2-- Copyright(C) 1998
 3-- All Rights Reserved. Salih Yurttas, ZCubes, BitsOfCode Software Systems, Inc..
 4--
 5-- Permission to use, copy, modify, and distribute this
 6-- software and its documentation for EDUCATIONAL purposes
 7-- and without fee is hereby granted provided that this
 8-- copyright notice appears in all copies.
 9--
10 
11-- date   : January 1, 1998.
12-- author : Salih Yurttas.
13
14-- queue_02_p.adb
15
16
17package body Queue_02_P is
18
19  subtype Queue_Index is Integer range 0..Queue_Size-1;
20
21  Queue_Head   : Queue_Index;
22  Queue_Length : Integer range 0..Queue_Size;
23  Queue_Body   : array(Queue_Index) of Element;
24
25  function Full return Boolean is
26  begin
27    return Queue_Length = Queue_Size;
28  end Full;
29
30  function Empty return Boolean is
31  begin
32    return Queue_Length = 0;
33  end Empty;
34
35  procedure Enqueue(E : in Element) is
36  begin 
37    if Full then
38      raise overflow;
39    end if;
40
41    Queue_Body((Queue_Head+Queue_Length) mod Queue_Size) := E;
42    Queue_Length := Queue_Length + 1;
43  end Enqueue;
44
45  function Dequeue return Element is
46    E : Element := Queue_Body(Queue_Head);
47  begin 
48    if Empty then
49      raise underflow;
50    end if;
51
52    Queue_Head := (Queue_Head+1) mod Queue_Size;
53    Queue_Length := Queue_Length - 1;
54
55    return E;
56  end Dequeue;
57
58begin
59
60  Queue_Head   := 0;
61  Queue_Length := 0;
62
63end Queue_02_P;