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      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> */
     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 
    104         public virtual void Enqueue(T o) {
    105             _data.Add(o);
    106         }
    107 
    108         public virtual T Peek() {
    109             return this[0];
    110         }
    111 
    112         public virtual void Clear() {
    113             _p = 0;
    114             _data.Clear();
    115         }
    116 
    117         /** <summary>Return string of current buffer contents; non-destructive</summary> */
    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