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 {
35     using System.Collections.Generic;
36     using ArgumentException = System.ArgumentException;
37     using InvalidOperationException = System.InvalidOperationException;
38 
39     /** A queue that can dequeue and get(i) in O(1) and grow arbitrarily large.
40      *  A linked list is fast at dequeue but slow at get(i).  An array is
41      *  the reverse.  This is O(1) for both operations.
42      *
43      *  List grows until you dequeue last element at end of buffer. Then
44      *  it resets to start filling at 0 again.  If adds/removes are balanced, the
45      *  buffer will not grow too large.
46      *
47      *  No iterator stuff as that's not how we'll use it.
48      */
49     public class FastQueue<T>
50     {
51         /** <summary>dynamically-sized buffer of elements</summary> */
52         internal List<T> _data = new List<T>();
53         /** <summary>index of next element to fill</summary> */
54         internal int _p = 0;
55 
56         public virtual int Count
57         {
58             get
59             {
60                 return _data.Count - _p;
61             }
62         }
63 
64         /// <summary>
65         /// How deep have we gone?
66         /// </summary>
67         public virtual int Range
68         {
69             get;
70             protected set;
71         }
72 
73         /** <summary>
74          *  Return element i elements ahead of current element.  i==0 gets
75          *  current element.  This is not an absolute index into the data list
76          *  since p defines the start of the real list.
77          *  </summary>
78          */
79         public virtual T this[int i]
80         {
81             get
82             {
83                 int absIndex = _p + i;
84                 if (absIndex >= _data.Count)
85                     throw new ArgumentException(string.Format("queue index {0} > last index {1}", absIndex, _data.Count - 1));
86                 if (absIndex < 0)
87                     throw new ArgumentException(string.Format("queue index {0} < 0", absIndex));
88 
89                 if (absIndex > Range)
90                     Range = absIndex;
91 
92                 return _data[absIndex];
93             }
94         }
95 
96         /** <summary>Get and remove first element in queue</summary> */
Dequeue()97         public virtual T Dequeue()
98         {
99             if (Count == 0)
100                 throw new InvalidOperationException();
101 
102             T o = this[0];
103             _p++;
104             // have we hit end of buffer?
105             if ( _p == _data.Count )
106             {
107                 // if so, it's an opportunity to start filling at index 0 again
108                 Clear(); // size goes to 0, but retains memory
109             }
110             return o;
111         }
112 
Enqueue( T o )113         public virtual void Enqueue( T o )
114         {
115             _data.Add( o );
116         }
117 
Peek()118         public virtual T Peek()
119         {
120             return this[0];
121         }
122 
Clear()123         public virtual void Clear()
124         {
125             _p = 0;
126             _data.Clear();
127         }
128 
129         /** <summary>Return string of current buffer contents; non-destructive</summary> */
ToString()130         public override string ToString()
131         {
132             System.Text.StringBuilder buf = new System.Text.StringBuilder();
133             int n = Count;
134             for ( int i = 0; i < n; i++ )
135             {
136                 buf.Append( this[i] );
137                 if ( ( i + 1 ) < n )
138                     buf.Append( " " );
139             }
140             return buf.ToString();
141         }
142     }
143 }
144