private static void StableSortInternal <T>(
IList <T> list,
int a,
int n,
IComparer <T> comparer,
DeferredArray <T> tempArray)
{
#if DEBUG
if (list == null)
{
throw new ArgumentNullException("list");
}
if (a < 0)
{
throw new ArgumentException("a (" + a + ") is less than 0");
}
if (a > list.Count)
{
throw new ArgumentException("a (" + a + ") is more than " + list.Count);
}
if (n < 0)
{
throw new ArgumentException("n (" + n + ") is less than 0");
}
if (n > list.Count)
{
throw new ArgumentException("n (" + n + ") is more than " + list.Count);
}
if (list.Count - a < n)
{
throw new ArgumentException("list's length minus " + a + " (" +
(list.Count - a) + ") is less than " + n);
}
if (comparer == null)
{
throw new ArgumentNullException("comparer");
}
#endif
int pl, pm;
T tmp;
if (n < 7)
{
// Use insertion sort (already a stable sort)
for (pm = a + 1; pm < a + n; ++pm)
{
for (pl = pm; pl > a && comparer.Compare(list[pl - 1], list[pl]) > 0; --pl)
{
tmp = list[pl];
list[pl] = list[pl - 1];
list[pl - 1] = tmp;
}
}
return;
}
var middle = n >> 1;
StableSortInternal(list, a, middle, comparer, tempArray);
StableSortInternal(list, a + middle, n - middle, comparer, tempArray);
if (comparer.Compare(list[a + middle - 1], list[a + middle]) <= 0)
{
return;
}
var right = a + n;
middle = a + middle;
var temp = tempArray.GetArray();
var i = a;
var j = a;
var k = middle;
while (j < middle && k < right)
{
// "<=" ensures stable sort
var leq = comparer.Compare(list[j], list[k]) <= 0;
temp[i++] = leq ? list[j++] : list[k++];
}
while (j < middle)
{
temp[i++] = list[j++];
}
for (i = a; i < k; ++i)
{
list[i] = temp[i];
}
}
