1 /*
2  * [The "BSD licence"]
3  * Copyright (c) 2005-2008 Terence Parr
4  * All rights reserved.
5  *
6  * Conversion to C#:
7  * Copyright (c) 2008-2009 Sam Harwell, Pixel Mine, Inc.
8  * All rights reserved.
9  *
10  * Redistribution and use in source and binary forms, with or without
11  * modification, are permitted provided that the following conditions
12  * are met:
13  * 1. Redistributions of source code must retain the above copyright
14  *    notice, this list of conditions and the following disclaimer.
15  * 2. Redistributions in binary form must reproduce the above copyright
16  *    notice, this list of conditions and the following disclaimer in the
17  *    documentation and/or other materials provided with the distribution.
18  * 3. The name of the author may not be used to endorse or promote products
19  *    derived from this software without specific prior written permission.
20  *
21  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
22  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
23  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
24  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
25  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
26  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
27  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
28  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
29  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
30  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
31  */
32 
33 namespace Antlr.Runtime.Misc {
34     using System.Collections.Generic;
35     using ArgumentException = System.ArgumentException;
36     using InvalidOperationException = System.InvalidOperationException;
37 
38     /** A queue that can dequeue and get(i) in O(1) and grow arbitrarily large.
39      *  A linked list is fast at dequeue but slow at get(i).  An array is
40      *  the reverse.  This is O(1) for both operations.
41      *
42      *  List grows until you dequeue last element at end of buffer. Then
43      *  it resets to start filling at 0 again.  If adds/removes are balanced, the
44      *  buffer will not grow too large.
45      *
46      *  No iterator stuff as that's not how we'll use it.
47      */
48     public class FastQueue<T> {
49         /** <summary>dynamically-sized buffer of elements</summary> */
50         internal List<T> _data = new List<T>();
51         /** <summary>index of next element to fill</summary> */
52         internal int _p = 0;
53 
54         public virtual int Count {
55             get {
56                 return _data.Count - _p;
57             }
58         }
59 
60         /// <summary>
61         /// How deep have we gone?
62         /// </summary>
63         public virtual int Range {
64             get;
65             protected set;
66         }
67 
68         /** <summary>
69          *  Return element i elements ahead of current element.  i==0 gets
70          *  current element.  This is not an absolute index into the data list
71          *  since p defines the start of the real list.
72          *  </summary>
73          */
74         public virtual T this[int i] {
75             get {
76                 int absIndex = _p + i;
77                 if (absIndex >= _data.Count)
78                     throw new ArgumentException(string.Format("queue index {0} > last index {1}", absIndex, _data.Count - 1));
79                 if (absIndex < 0)
80                     throw new ArgumentException(string.Format("queue index {0} < 0", absIndex));
81 
82                 if (absIndex > Range)
83                     Range = absIndex;
84 
85                 return _data[absIndex];
86             }
87         }
88 
89         /** <summary>Get and remove first element in queue</summary> */
Dequeue()90         public virtual T Dequeue() {
91             if (Count == 0)
92                 throw new InvalidOperationException();
93 
94             T o = this[0];
95             _p++;
96             // have we hit end of buffer?
97             if (_p == _data.Count) {
98                 // if so, it's an opportunity to start filling at index 0 again
99                 Clear(); // size goes to 0, but retains memory
100             }
101             return o;
102         }
103 
Enqueue(T o)104         public virtual void Enqueue(T o) {
105             _data.Add(o);
106         }
107 
Peek()108         public virtual T Peek() {
109             return this[0];
110         }
111 
Clear()112         public virtual void Clear() {
113             _p = 0;
114             _data.Clear();
115         }
116 
117         /** <summary>Return string of current buffer contents; non-destructive</summary> */
ToString()118         public override string ToString() {
119             System.Text.StringBuilder buf = new System.Text.StringBuilder();
120             int n = Count;
121             for (int i = 0; i < n; i++) {
122                 buf.Append(this[i]);
123                 if ((i + 1) < n)
124                     buf.Append(" ");
125             }
126             return buf.ToString();
127         }
128     }
129 }
130