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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 {
     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> */
     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 
    113         public virtual void Enqueue( T o )
    114         {
    115             _data.Add( o );
    116         }
    117 
    118         public virtual T Peek()
    119         {
    120             return this[0];
    121         }
    122 
    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> */
    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