FastQueue

internal class FastQueue<T> where T : struct
{
    public T[] items;
    public int mask;
    public uint tail, head;

    public FastQueue(int capacity = 16)
    {
        capacity = 1 << (int) Math.Ceiling(Math.Log(capacity, 2)); // calculate closest power of two
        items = new T[capacity];
        mask = capacity - 1;
        tail = head = 0;
    }

    public int Count
    {
        get { return (int) (tail - head); }
    }

    public void Enqueue(T item)
    {
        if (tail - head == items.Length)
        {
            DoubleCapacity();
        }

        items[tail++ & mask] = item;
    }

    public void FastEnqueue(T item)
    {
        items[tail++ & mask] = item;
    }

    public T Dequeue()
    {
        return items[head++ & mask];
    }

    private void DoubleCapacity()
    {
        var capacity = items.Length << 1;

        if ((head & mask) == 0)
        {
            Array.Resize(ref items, capacity);
        }
        else
        {
            int size = items.Length;
            var items2 = new T[capacity];
            int length = (int) (size - head & mask);
            Array.Copy(items, head & mask, items2, 0, length);
            Array.Copy(items, 0, items2, length, size - length);

            items = items2;
            head = 0;
            tail = (uint) size;
        }

        mask = capacity - 1;
    }
}