attempt at qsort implementation

From: buda (kulghan_at_hotmail.com)
Date: 09/28/04 

Date: Tue, 28 Sep 2004 20:42:04 +0200

I had some spare time and decided to try to implement the standard library
qsort. This is a pretty simpleminded attempt, but it seems to be working. I
have to point out that efficiency is not at all an issue for me, and this is
purely a toy, so to speak. I'm quite aware that this is not the quickest way
to implement the quicksort algorithm, but I basically just wanted to try to
make a "generic function". I tested it with a few arrays of structures
containing all sorts of types (this, ofcourse, doesn't mean that it's
correct, even by a long shot :). I would appreciate any and all constructive
comments. The code below is a snippet. All the necessary headers are
included and uchar is a typedef for unsigned char.
Thank you.

void do_swap_(void *a, void *b, size_t sz)
{
  uchar t;
  uchar *i = a;
  uchar *j = b;

  while (sz) {
    t = *i;
    *i++ = *j;
    *j++ = t;
    --sz;
  }
}
void quick_sort(void *v, size_t count, size_t sz, int (*cmp)(const void *,
const void *))
{
  uchar *t = v;
  uchar *x, *y;
  uchar *r;

  if (count) {
    x = y = t;
    r = t+(count-1)*sz;
    for(; y<r; y += sz)
      if (cmp(y, r)<0) {
        do_swap_(x, y, sz);
        x += sz;
      }
    do_swap_(x, r, sz);
    quick_sort(t, (x-t)/sz, sz, cmp);
    quick_sort(x+sz, count-(x-t)/sz - 1, sz, cmp);
  }
}