I have a need for an efficient sort that doesn't have a callback, but is as customizable as using qsort(). What I want is for it to work like an iterator, where it continuously calls into the sort API in a loop until it is done, doing the comparison in the loop rather than off in a callback function. This way the custom comparison is local to the calling function (and therefore has access to local variables, is potentially more efficient, etc). I have implemented this for an inefficient selection sort, but need it to be efficient, so prefer a quick sort derivative.

Has anyone done anything like this? I tried to do it for quick sort, but trying to turn the algorithm inside out hurt my brain too much.

Below is how it might look in use.

// the array of data we are sorting
MyData array[5000], *firstP, *secondP;

// (assume data is filled in)

Sorter sorter;

// initialize sorter
int result = sortInit (&sorter, array, 5000,
        (void **)&firstP, (void **)&secondP, sizeof(MyData));

// loop until complete
while (sortIteration (&sorter, result) == 0) {
    // here's where we do the custom comparison...here we
    // just sort by member "value" but we could do anything
    result = firstP->value - secondP->value;
    }