QSort in D: is this best?

[Lutger]

downs wrote:

> Or are there any bugs/optimization opportunities I'm missing?
> 
> void qsort(T)(T[] array) {
>   if (array.length < 2) return;
>   static int i;
>   auto pivot = array[i++%$];
>   // from is base-0, to is base-1.
>   int from = 0, to = array.length;
>   while (from != to) {
>     if (array[from] >= pivot && array[to-1] < pivot)
>       swap(array[from], array[to-1]);
>     if (array[from] < pivot)
>       from ++;
>     if (array[to-1] >= pivot)
>       to --;
>   }
>   array[0 .. from].qsort();
>   array[from .. $].qsort();
> }

It's not reentrant but perhaps you don't care?

I think these two optimizations matter the most:
- improve selection of pivot (median of 3 for example)
- switch to insertion sort or shellsort when array is below a certain length 
(somewhere between 50 and 150 I think is ok). 

A further optimization can be to implement a custom stack, but it's not as 
much bang-for-buck as switching to a different sort.