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//-----------------------------------------------------------------------------
// Copyright (c) Microsoft Corporation. All rights reserved.
//-----------------------------------------------------------------------------
namespace System.Activities
{
using System;
using System.Runtime;
// A mostly output-restricted double-ended queue. You can add an item to both ends
// and it is optimized for removing from the front. The list can be scanned and
// items can be removed from any location at the cost of performance.
class Quack<T>
{
T[] items;
// First element when items is not empty
int head;
// Next vacancy when items are not full
int tail;
// Number of elements.
int count;
public Quack()
{
this.items = new T[4];
}
public Quack(T[] items)
{
Fx.Assert(items != null, "This shouldn't get called with null");
Fx.Assert(items.Length > 0, "This shouldn't be called with a zero length array.");
this.items = items;
// The default value of 0 is correct for both
// head and tail.
this.count = this.items.Length;
}
public int Count
{
get { return this.count; }
}
public T this[int index]
{
get
{
Fx.Assert(index < this.count, "Index out of range.");
int realIndex = (this.head + index) % this.items.Length;
return this.items[realIndex];
}
}
public T[] ToArray()
{
Fx.Assert(this.count > 0, "We should only call this when we have items.");
T[] compressedItems = new T[this.count];
for (int i = 0; i < this.count; i++)
{
compressedItems[i] = this.items[(this.head + i) % this.items.Length];
}
return compressedItems;
}
public void PushFront(T item)
{
if (this.count == this.items.Length)
{
Enlarge();
}
if (--this.head == -1)
{
this.head = this.items.Length - 1;
}
this.items[this.head] = item;
++this.count;
}
public void Enqueue(T item)
{
if (this.count == this.items.Length)
{
Enlarge();
}
this.items[this.tail] = item;
if (++this.tail == this.items.Length)
{
this.tail = 0;
}
++this.count;
}
public T Dequeue()
{
Fx.Assert(this.count > 0, "Quack is empty");
T removed = this.items[this.head];
this.items[this.head] = default(T);
if (++this.head == this.items.Length)
{
this.head = 0;
}
--this.count;
return removed;
}
public bool Remove(T item)
{
int found = -1;
for (int i = 0; i < this.count; i++)
{
int realIndex = (this.head + i) % this.items.Length;
if (object.Equals(this.items[realIndex], item))
{
found = i;
break;
}
}
if (found == -1)
{
return false;
}
else
{
Remove(found);
return true;
}
}
public void Remove(int index)
{
Fx.Assert(index < this.count, "Index out of range");
for (int i = index - 1; i >= 0; i--)
{
int sourceIndex = (this.head + i) % this.items.Length;
int targetIndex = sourceIndex + 1;
if (targetIndex == this.items.Length)
{
targetIndex = 0;
}
this.items[targetIndex] = this.items[sourceIndex];
}
--this.count;
++this.head;
if (this.head == this.items.Length)
{
this.head = 0;
}
}
void Enlarge()
{
Fx.Assert(this.items.Length > 0, "Quack is empty");
int capacity = this.items.Length * 2;
this.SetCapacity(capacity);
}
void SetCapacity(int capacity)
{
Fx.Assert(capacity >= this.count, "Capacity is set to a smaller value");
T[] newArray = new T[capacity];
if (this.count > 0)
{
if (this.head < this.tail)
{
Array.Copy(this.items, this.head, newArray, 0, this.count);
}
else
{
Array.Copy(this.items, this.head, newArray, 0, this.items.Length - this.head);
Array.Copy(this.items, 0, newArray, this.items.Length - this.head, this.tail);
}
}
this.items = newArray;
this.head = 0;
this.tail = (this.count == capacity) ? 0 : this.count;
}
}
}
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