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/*
*
* This file is part of
* MakeIndex - A formatter and format independent index processor
*
* This file is public domain software donated by
* Nelson Beebe (beebe@science.utah.edu).
*
*/
/*
* 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 "qsort.h" /* qq_compar_fn_t type and qqsort() prototype */
#define THRESH 4 /* threshold for insertion */
#define MTHRESH 6 /* threshold for median */
static int qsz; /* size of each record */
static int thresh; /* THRESHold in chars */
static int mthresh; /* MTHRESHold in chars */
static qq_compar_fn_t qcmp; /* the comparison routine */
static void qst(char *base, char *max);
/*
* qqsort: 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
qqsort(void *base, size_t n, size_t size, qq_compar_fn_t 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 = (char *)base + n * qsz;
if (n >= THRESH) {
qst(base, max);
hi = (char *)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 = i + 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(char *base, char *max)
{
register char *i;
register char *j;
register char *jj;
register char *mid;
register int ii;
register char c;
void *tmp;
size_t lo;
size_t 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) {
/* switch to first loser */
j = (j == jj ? i : jj);
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 updated 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);
}
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