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- /*
- * 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 <stdio.h> -- mkind.h includes this */
- #include "mkind.h" /* only for type declarations */
-
- #define THRESH 4 /* threshold for insertion */
- #define MTHRESH 6 /* threshold for median */
-
- static int (*qcmp) (); /* the comparison routine */
- static int qsz; /* size of each record */
-
- static int thresh; /* THRESHold in chars */
- static int mthresh; /* MTHRESHold in chars */
-
-
-
- /*
- * 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...
- */
-
- void
- qsort(base, n, size, compar)
- char *base;
- int n;
- int size;
- int (*compar) ();
- {
- register char *i;
- register char *j;
- register char *lo;
- register char *hi;
- register char *min;
- register char c;
- char *max;
-
- if (n <= 1)
- return;
- qsz = size;
- qcmp = compar;
- thresh = qsz * THRESH;
- mthresh = qsz * MTHRESH;
- max = base + n * qsz;
- 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 += qsz) < hi;)
- {
- if ((*qcmp) (j, lo) > 0)
- j = lo;
- }
- if (j != base)
- { /* swap j into place */
- for (i = base, hi = base + qsz; i < hi;)
- {
- c = *j;
- *j++ = *i;
- *i++ = c;
- }
- }
- /* 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 += qsz) < max;)
- {
- while ((*qcmp) (hi -= qsz, min) > 0);
- if ((hi += qsz) != min)
- {
- for (lo = min + qsz; --lo >= min;)
- {
- c = *lo;
- for (i = j = lo; (j -= qsz) >= hi; i = j)
- *i = *j;
- *i = c;
- }
- }
- }
- }
-
-
-
- /*
- * 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).
- */
-
- static void
- qst(base, max)
- char *base;
- char *max;
- {
- register char *i;
- register char *j;
- register char *jj;
- register char *mid;
- register int ii;
- register char c;
- char *tmp;
- int lo;
- int 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 + qsz * ((unsigned) (lo / qsz) >> 1);
- if (lo >= mthresh)
- {
- j = ((*qcmp) ((jj = base), i) > 0 ? jj : i);
- if ((*qcmp) (j, (tmp = max - qsz)) > 0)
- {
- j = (j == jj ? i : jj); /* switch to first loser */
- if ((*qcmp) (j, tmp) < 0)
- j = tmp;
- }
- if (j != i)
- {
- ii = qsz;
- do
- {
- c = *i;
- *i++ = *j;
- *j++ = c;
- } while (--ii);
- }
- }
- /* Semi-standard quicksort partitioning/swapping */
- for (i = base, j = max - qsz;;)
- {
- while (i < mid && (*qcmp) (i, mid) <= 0)
- i += qsz;
- while (j > mid)
- {
- if ((*qcmp) (mid, j) <= 0)
- {
- j -= qsz;
- continue;
- }
- tmp = i + qsz; /* value of i after swap */
- if (i == mid)
- { /* j <-> mid, new mid is j */
- mid = jj = j;
- }
- else
- { /* i <-> j */
- jj = j;
- j -= qsz;
- }
- goto swap;
- }
- if (i == mid)
- {
- break;
- }
- else
- { /* i <-> mid, new mid is i */
- jj = mid;
- tmp = mid = i; /* value of i after swap */
- j -= qsz;
- }
- swap:
- ii = qsz;
- do
- {
- c = *i;
- *i++ = *jj;
- *jj++ = c;
- } while (--ii);
- 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) + qsz;
- 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);
- }
-