private static void Sort(IComparable[] a, int lo, int hi)
{
int N = hi - lo + 1;
// cutoff to insertion sort
if (N <= CUTOFF)
{
Insertion.Sort(a, lo, hi);
return;
}
// use median-of-3 as partitioning element
else if (N <= 40)
{
int m = median3(a, lo, lo + N / 2, hi);
OrderHelper.Exch(a, m, lo);
}
// use Tukey ninther as partitioning element
else
{
int eps = N / 8;
int mid = lo + N / 2;
int m1 = median3(a, lo, lo + eps, lo + eps + eps);
int m2 = median3(a, mid - eps, mid, mid + eps);
int m3 = median3(a, hi - eps - eps, hi - eps, hi);
int ninther = median3(a, m1, m2, m3);
OrderHelper.Exch(a, ninther, lo);
}
// Bentley-McIlroy 3-way partitioning
int i = lo, j = hi + 1;
int p = lo, q = hi + 1;
IComparable v = a[lo];
while (true)
{
while (OrderHelper.Less(a[++i], v))
{
if (i == hi)
{
break;
}
}
while (OrderHelper.Less(v, a[--j]))
{
if (j == lo)
{
break;
}
}
// pointers cross
if (i == j && OrderHelper.Eq(a[i], v))
{
OrderHelper.Exch(a, ++p, i);
}
if (i >= j)
{
break;
}
OrderHelper.Exch(a, i, j);
if (OrderHelper.Eq(a[i], v))
{
OrderHelper.Exch(a, ++p, i);
}
if (OrderHelper.Eq(a[j], v))
{
OrderHelper.Exch(a, --q, j);
}
}
i = j + 1;
for (int k = lo; k <= p; k++)
{
OrderHelper.Exch(a, k, j--);
}
for (int k = hi; k >= q; k--)
{
OrderHelper.Exch(a, k, i++);
}
Sort(a, lo, j);
Sort(a, i, hi);
}
