void
ruby_qsort(void* base, const size_t nel, const size_t size, cmpfunc_t *cmp, void *d)
{
  register char *l, *r, *m;          	/* l,r:left,right group   m:median point */
  register int t, eq_l, eq_r;       	/* eq_l: all items in left group are equal to S */
  char *L = base;                    	/* left end of current region */
  char *R = (char*)base + size*(nel-1); /* right end of current region */
  size_t chklim = 63;                   /* threshold of ordering element check */
  stack_node stack[32], *top = stack;   /* 32 is enough for 32bit CPU */
  int mmkind;
  size_t high, low, n;

  if (nel <= 1) return;        /* need not to sort */
  mmprepare(base, size);
  goto start;

  nxt:
  if (stack == top) return;    /* return if stack is empty */
  POP(L,R);

  for (;;) {
    start:
    if (L + size == R) {       /* 2 elements */
      if ((*cmp)(L,R,d) > 0) mmswap(L,R); goto nxt;
    }

    l = L; r = R;
    n = (r - l + size) / size;  /* number of elements */
    m = l + size * (n >> 1);    /* calculate median value */

    if (n >= 60) {
      register char *m1;
      register char *m3;
      if (n >= 200) {
	n = size*(n>>3); /* number of bytes in splitting 8 */
	{
	  register char *p1 = l  + n;
	  register char *p2 = p1 + n;
	  register char *p3 = p2 + n;
	  m1 = med3(p1, p2, p3);
	  p1 = m  + n;
	  p2 = p1 + n;
	  p3 = p2 + n;
	  m3 = med3(p1, p2, p3);
	}
      }
      else {
	n = size*(n>>2); /* number of bytes in splitting 4 */
	m1 = l + n;
	m3 = m + n;
      }
      m = med3(m1, m, m3);
    }

    if ((t = (*cmp)(l,m,d)) < 0) {                           /*3-5-?*/
      if ((t = (*cmp)(m,r,d)) < 0) {                         /*3-5-7*/
	if (chklim && nel >= chklim) {   /* check if already ascending order */
	  char *p;
	  chklim = 0;
	  for (p=l; p<r; p+=size) if ((*cmp)(p,p+size,d) > 0) goto fail;
	  goto nxt;
	}
	fail: goto loopA;                                    /*3-5-7*/
      }
      if (t > 0) {
	if ((*cmp)(l,r,d) <= 0) {mmswap(m,r); goto loopA;}     /*3-5-4*/
	mmrot3(r,m,l); goto loopA;                           /*3-5-2*/
      }
      goto loopB;                                            /*3-5-5*/
    }

    if (t > 0) {                                             /*7-5-?*/
      if ((t = (*cmp)(m,r,d)) > 0) {                         /*7-5-3*/
	if (chklim && nel >= chklim) {   /* check if already ascending order */
	  char *p;
	  chklim = 0;
	  for (p=l; p<r; p+=size) if ((*cmp)(p,p+size,d) < 0) goto fail2;
	  while (l<r) {mmswap(l,r); l+=size; r-=size;}  /* reverse region */
	  goto nxt;
	}
	fail2: mmswap(l,r); goto loopA;                      /*7-5-3*/
      }
      if (t < 0) {
	if ((*cmp)(l,r,d) <= 0) {mmswap(l,m); goto loopB;}   /*7-5-8*/
	mmrot3(l,m,r); goto loopA;                           /*7-5-6*/
      }
      mmswap(l,r); goto loopA;                               /*7-5-5*/
    }

    if ((t = (*cmp)(m,r,d)) < 0)  {goto loopA;}              /*5-5-7*/
    if (t > 0) {mmswap(l,r); goto loopB;}                    /*5-5-3*/

    /* determining splitting type in case 5-5-5 */           /*5-5-5*/
    for (;;) {
      if ((l += size) == r)      goto nxt;                   /*5-5-5*/
      if (l == m) continue;
      if ((t = (*cmp)(l,m,d)) > 0) {mmswap(l,r); l = L; goto loopA;}/*575-5*/
      if (t < 0)                 {mmswap(L,l); l = L; goto loopB;}  /*535-5*/
    }

    loopA: eq_l = 1; eq_r = 1;  /* splitting type A */ /* left <= median < right */
    for (;;) {
      for (;;) {
	if ((l += size) == r)
	  {l -= size; if (l != m) mmswap(m,l); l -= size; goto fin;}
	if (l == m) continue;
	if ((t = (*cmp)(l,m,d)) > 0) {eq_r = 0; break;}
	if (t < 0) eq_l = 0;
      }
      for (;;) {
	if (l == (r -= size))
	  {l -= size; if (l != m) mmswap(m,l); l -= size; goto fin;}
	if (r == m) {m = l; break;}
	if ((t = (*cmp)(r,m,d)) < 0) {eq_l = 0; break;}
	if (t == 0) break;
      }
      mmswap(l,r);    /* swap left and right */
    }

    loopB: eq_l = 1; eq_r = 1;  /* splitting type B */ /* left < median <= right */
    for (;;) {
      for (;;) {
	if (l == (r -= size))
	  {r += size; if (r != m) mmswap(r,m); r += size; goto fin;}
	if (r == m) continue;
	if ((t = (*cmp)(r,m,d)) < 0) {eq_l = 0; break;}
	if (t > 0) eq_r = 0;
      }
      for (;;) {
	if ((l += size) == r)
	  {r += size; if (r != m) mmswap(r,m); r += size; goto fin;}
	if (l == m) {m = r; break;}
	if ((t = (*cmp)(l,m,d)) > 0) {eq_r = 0; break;}
	if (t == 0) break;
      }
      mmswap(l,r);    /* swap left and right */
    }

    fin:
    if (eq_l == 0)                         /* need to sort left side */
      if (eq_r == 0)                       /* need to sort right side */
	if (l-L < R-r) {PUSH(r,R); R = l;} /* sort left side first */
	else           {PUSH(L,l); L = r;} /* sort right side first */
      else R = l;                          /* need to sort left side only */
    else if (eq_r == 0) L = r;             /* need to sort right side only */
    else goto nxt;                         /* need not to sort both sides */
  }