// Source: "Software Design ...", John A Robinson, Newnes, 2004, page 231.
void quicksort(int *start, int *end);	// Just the prototype
int sort(int *array, const int num_in_array)	// Wrapper for quicksort
	{
	quicksort(array, array + num_in_array - 1);
	return(0);
	}
void quicksort(int *start, int *end)		// The real thing
	{
	int *p, *q;
	int *centre;
	int pivot;
	if (end <= start)
		return;
	if (end == start + 1)
		{
		if (*end < *start)
			swap(end,start);
		return;
		}
	// At least three elements; do median of three to get pivot
	centre = start + (end-start)/2;
	if (*start > *centre)
		swap(start,centre);
	if (*start > *end)
		swap(start, end);
	if (*centre > *end)
		swap(centre, end);
	// Now with *centre as pivot, *start and *end are certainly
	// in the correct partitions.
	if (end == start + 2)
		return;
	// Get pivot value, then put pivot element out of the way
	pivot = *centre;
	swap(centre,end-1);
	p = start;
	q = end-1;
	// Now ready to partition the rest of the array
	while(1)
		{
		while(*++p < pivot);
		while(*--q > pivot);
		if (p >= q)
			break;
		swap(p,q);
		}
	// Finally put pivot element in its place
	swap(p,end-1);
	// And call recursively to do subarrays
	quicksort(start,p-1);
	quicksort(p+1,end);
	}