>Adding an extension method ( say AddCollection) is a bad idea since it accepts an argument of IEnumerable(T).
>
>using items.Count() is slow - I guess it uses a foreach loop to count
>
>

>// don't do this at home
>
>public static void AddCollection<T>(this List<T> list, IEnumerable<T> items)
>		{
>
>			if (items.Count() <= Tuning.AddRangeMinimumItems) // 128
>			{
>				foreach (T item in items)
>					list.Add(item);
>			}
>			else
>			{
>				list.AddRange(items);
>			}
>		}
>

>
>An extension method that takes a whole array is a better idea - since array.Length is faster

Gregory,
Sorry I didn't read the whole thread to see your purpose and solutions so far, could you use and try Linq Concat()? ie:

	public static void AddCollection<T>(this List<T> list, IEnumerable<T> items)
	{
			list.Concat( items );
	}

Update: I made a short test with this using your original test and probably I am doing something wrong, results are unbelievably fast:

00:00:05.5402003 // UseAddRange
00:00:01.9798588 // UseForeach
00:00:00.3055594 // UseConcat

Thinking F# power and sequence processing behind Linq that result might be perfectly right. Here is my UseConcat BTW:

       static void UseConcat()
        {
            int[] buf = new int[Size];
            List<int> list = new List<int>();
            for (int i = nTimes; --i != 0; )
            {
                list.AddCollection(buf);
                list.Clear();
            }

        }

Cetin