/*
 * qsort.c:
 * Our own version of the system qsort routine which is faster by an average
 * of 25%, with lows and highs of 10% and 50%.
 * The THRESHold below is the insertion sort threshold, and has been adjusted
 * for records of size 48 bytes.
 * The MTHREShold is where we stop finding a better median.
 */
#include "element.h"

#define		MTHRESH		6		/* threshold for median */

/*
 * qsort:
 * First, set up some global parameters for qst to share.  Then, quicksort
 * with qst(), and then a cleanup insertion sort ourselves.  Sound simple?
 * It's not...
 */


static int comparison(element *s1,element *s2)
{
  int d,j=0;
  do {
    if ((d=s1->c[j] - s2->c[j])) return(d);
  } while (++j<ELSIZE);
  return(0);
}


#define	THRESH 16
#define COMPARE(i1,i2) comparison((element *)(i1),(element *)(i2))
#define SWAPP(i1,i2) \
  {element itmp;itmp=*(element *)(i1);*(element *)(i1)=*(element *)(i2);*(element *)(i2)=itmp;}

void qst();

void gnu_qsort (base, n, size, compar)
     element *base;
     int n;
     int size;
     int (*compar)();
{
  element *i, *j, *lo, *hi, *min;
  element *max;

  if (n <= 1)  return;
  max = base + n;
  if (n >= THRESH)
    {
      qst (base, max);
      hi = base + THRESH;
    }
  else
    {
      hi = max;
    }
  /*
   * First put smallest element, which must be in the first THRESH, in
   * the first position as a sentinel.  This is done just by searching
   * the first THRESH elements (or the first n if n < THRESH), finding
   * the min, and swapping it into the first position.
   */
  for (j = lo = base; (lo += 1) < hi; )
    {
      if (COMPARE(j, lo) > 0)
	j = lo;
    }
  if (j != base)
    {			/* swap j into place */
      for (i = base, hi = base + 1; i < hi;)
      {
	SWAPP(i,j);
	i+=1;j+=1;
      }
    }
  /*
   * With our sentinel in place, we now run the following hyper-fast
   * insertion sort.  For each remaining element, min, from [1] to [n-1],
   * set hi to the index of the element AFTER which this one goes.
   * Then, do the standard insertion sort shift on a character at a time
   * basis for each element in the frob.
   */
  for (min = base; (hi = min += 1) < max;)
    {
      while ( COMPARE(hi -= 1, min) > 0);

      if ((hi += 1) != min)
      {
	element cI;
	element *loI,*minI=(element *)min,*hiI=(element *)hi,*iI,*jI;
	for (loI = minI + 1; --loI >= minI;)
	  {
	    cI = *loI;
	    for (iI = jI = loI; (jI -= 1) >= hiI; iI = jI)
	      *iI = *jI;
	    *iI = cI;
	  }
      }
    }
}

/*
 * qst:
 * Do a quicksort
 * First, find the median element, and put that one in the first place as the
 * discriminator.  (This "median" is just the median of the first, last and
 * middle elements).  (Using this median instead of the first element is a big
 * win).  Then, the usual partitioning/swapping, followed by moving the
 * discriminator into the right place.  Then, figure out the sizes of the two
 * partions, do the smaller one recursively and the larger one via a repeat of
 * this code.  Stopping when there are less than THRESH elements in a partition
 * and cleaning up with an insertion sort (in our caller) is a huge win.
 * All data swaps are done in-line, which is space-losing but time-saving.
 * (And there are only three places where this is done).
 */

void qst (base, max)
     element *base, *max;
{
  element *i, *j, *jj, *mid;
  element *tmp;
  int lo, hi;

  lo = max - base;		/* number of elements as chars */
  do
    {
      /*
       * At the top here, lo is the number of characters of elements in the
       * current partition.  (Which should be max - base).
       * Find the median of the first, last, and middle element and make that the
       * middle element.  Set j to largest of first and middle.  If max is larger
       * than that guy, then it's that guy, else compare max with loser of first
       * and take larger.  Things are set up to prefer the middle, then the first
       * in case of ties.
       */
      mid = i = base + (lo >> 1);
      if (lo >= MTHRESH)
	{
	  jj = base;
	  j = (COMPARE(jj, i) > 0 ? jj : i);
	  tmp = max - 1;
	  if (COMPARE(j, tmp) > 0)
	    {
	      j = (j == jj ? i : jj);	/* switch to first loser */
	      if (COMPARE(j, tmp) < 0)
		j = tmp;
	    }
	  if (j != i)
	    {
	      SWAPP(i,j);
	      i+=1;j+=1;
	    }
	}
      /*
       * Semi-standard quicksort partitioning/swapping
       */
      for (i = base, j = max - 1; ;)
	{
	  while (i < mid && COMPARE(i, mid) <= 0)
	    i += 1;
	  while (j > mid)
	    {
	      if (COMPARE(mid, j) <= 0)
		{
		  j -= 1;
		  continue;
		}
	      tmp = i + 1;		/* value of i after swap */
	      if (i == mid)
		{	/* j <-> mid, new mid is j */
		  mid = jj = j;
		}
	      else
		{			/* i <-> j */
		  jj = j;
		  j -= 1;
		}
	      goto swap;
	    }
	  if (i == mid)
	    {
	      break;
	    }
	  else
	    {				/* i <-> mid, new mid is i */
	      jj = mid;
	      tmp = mid = i;		/* value of i after swap */
	      j -= 1;
	    }
	swap:
	  SWAPP(i,jj);
	  i = tmp;
	}
      /*
       * Look at sizes of the two partitions, do the smaller one first by
       * recursion, then do the larger one by making sure lo is its size,
       * base and max are update correctly, and branching back.
       * But only repeat (recursively or by branching) if the partition is
       * of at least size THRESH.
       */
      i = (j = mid) + 1;
      if ((lo = j - base) <= (hi = max - i))
	{
	  if (lo >= THRESH)
	    qst (base, j);
	  base = i;
	  lo = hi;
	}
      else
	{
	  if (hi >= THRESH)
	    qst (i, max);
	  max = j;
	}
    }
  while (lo >= THRESH);
}



void rsort(char *base,int n)
{
  gnu_qsort(base,n,ELSIZE,comparison);
}