/// <summary>
/// Removes items from the instance.
/// </summary>
/// <param name="itemCount">Number of items to remove</param>
/// <returns></returns>
/// <remarks>DO NOT dispose the original and then slice. Either the original or the sliced instance can be disposed, but not both.</remarks>
public Multispan <T> Slice(int itemCount)
{
var result = new Multispan <T>();
var first = GetAt(0);
// if the only thing needing slicing is the head
if (first.Count > itemCount)
{
result._head = _head.Slice(itemCount);
result._count = _count;
if (Count > 1)
{
EnsureTailCapacity(ref result, _count - 1);
Array.Copy(_tail, result._tail, _count - 1);
}
return(result);
}
// head will be removed; this computes how many tail segments need to be removed
// and how many items from the first segment that is not removed
var itemsLeftToRemove = itemCount - first.Count;
int tailSegmentsToRemove = 1; // one is moved to the head
for (int tailIndex = 0; tailIndex < _count - 1; tailIndex++)
{
if (itemsLeftToRemove == 0)
{
break;
}
var segment = _tail[tailIndex];
if (segment.Count >= itemsLeftToRemove)
{
break;
}
else
{
tailSegmentsToRemove++;
itemsLeftToRemove -= segment.Count;
}
}
result._head = _tail[tailSegmentsToRemove - 1].Slice(itemsLeftToRemove);
result._count = _count - tailSegmentsToRemove;
if (result._count == 1)
{
return(result); // we don't need tail; this multispan has just head
}
EnsureTailCapacity(ref result, result._count - 1);
Array.Copy(_tail, tailSegmentsToRemove, result._tail, 0, result._count - 1);
return(result);
}
private static void EnsureTailCapacity(ref Multispan <T> ms, int count)
{
int desired = (ms._tail == null) ? 4 : ms._tail.Length * 2;
while (desired < count)
{
desired = desired * 2;
}
var newSegments = ArrayPool <ArraySegment <T> > .Shared.Rent(desired);
if (ms._tail != null)
{
ms._tail.CopyTo(newSegments, 0);
ArrayPool <ArraySegment <T> > .Shared.Return(ms._tail);
}
ms._tail = newSegments;
}
internal Enumerator(Multispan <T> buffer)
{
_buffer = buffer;
_index = -1;
}