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      1 /*
      2  * CDDL HEADER START
      3  *
      4  * The contents of this file are subject to the terms of the
      5  * Common Development and Distribution License, Version 1.0 only
      6  * (the "License").  You may not use this file except in compliance
      7  * with the License.
      8  *
      9  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
     10  * or http://www.opensolaris.org/os/licensing.
     11  * See the License for the specific language governing permissions
     12  * and limitations under the License.
     13  *
     14  * When distributing Covered Code, include this CDDL HEADER in each
     15  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     16  * If applicable, add the following below this CDDL HEADER, with the
     17  * fields enclosed by brackets "[]" replaced with your own identifying
     18  * information: Portions Copyright [yyyy] [name of copyright owner]
     19  *
     20  * CDDL HEADER END
     21  */
     22 /*
     23  * Copyright 1990 Sun Microsystems, Inc.  All rights reserved.
     24  * Use is subject to license terms.
     25  */
     26 
     27 #pragma ident	"%Z%%M%	%I%	%E% SMI"
     28 
     29 /*
     30  * qsort.c:
     31  * Our own version of the system qsort routine which is faster by an average
     32  * of 25%, with lows and highs of 10% and 50%.
     33  * The THRESHold below is the insertion sort threshold, and has been adjusted
     34  * for records of size 48 bytes.
     35  * The MTHREShold is where we stop finding a better median.
     36  */
     37 
     38 #define		THRESH		4		/* threshold for insertion */
     39 #define		MTHRESH		6		/* threshold for median */
     40 
     41 static  int		(*qcmp)();		/* the comparison routine */
     42 static  int		qsz;			/* size of each record */
     43 static  int		thresh;			/* THRESHold in chars */
     44 static  int		mthresh;		/* MTHRESHold in chars */
     45 
     46 static void	qst(char *, char *);
     47 
     48 /*
     49  * qsort:
     50  * First, set up some global parameters for qst to share.  Then, quicksort
     51  * with qst(), and then a cleanup insertion sort ourselves.  Sound simple?
     52  * It's not...
     53  */
     54 
     55 void
     56 qsort(char *base, int n, int size, int (*compar)())
     57 {
     58 	char c, *i, *j, *lo, *hi;
     59 	char *min, *max;
     60 
     61 	if (n <= 1)
     62 		return;
     63 	qsz = size;
     64 	qcmp = compar;
     65 	thresh = qsz * THRESH;
     66 	mthresh = qsz * MTHRESH;
     67 	max = base + n * qsz;
     68 	if (n >= THRESH) {
     69 		qst(base, max);
     70 		hi = base + thresh;
     71 	} else {
     72 		hi = max;
     73 	}
     74 	/*
     75 	 * First put smallest element, which must be in the first THRESH, in
     76 	 * the first position as a sentinel.  This is done just by searching
     77 	 * the first THRESH elements (or the first n if n < THRESH), finding
     78 	 * the min, and swapping it into the first position.
     79 	 */
     80 	for (j = lo = base; (lo += qsz) < hi; )
     81 		if (qcmp(j, lo) > 0)
     82 			j = lo;
     83 	if (j != base) {
     84 		/* swap j into place */
     85 		for (i = base, hi = base + qsz; i < hi; ) {
     86 			c = *j;
     87 			*j++ = *i;
     88 			*i++ = c;
     89 		}
     90 	}
     91 	/*
     92 	 * With our sentinel in place, we now run the following hyper-fast
     93 	 * insertion sort.  For each remaining element, min, from [1] to [n-1],
     94 	 * set hi to the index of the element AFTER which this one goes.
     95 	 * Then, do the standard insertion sort shift on a character at a time
     96 	 * basis for each element in the frob.
     97 	 */
     98 	for (min = base; (hi = min += qsz) < max; ) {
     99 		while (qcmp(hi -= qsz, min) > 0)
    100 			/* void */;
    101 		if ((hi += qsz) != min) {
    102 			for (lo = min + qsz; --lo >= min; ) {
    103 				c = *lo;
    104 				for (i = j = lo; (j -= qsz) >= hi; i = j)
    105 					*i = *j;
    106 				*i = c;
    107 			}
    108 		}
    109 	}
    110 }
    111 
    112 /*
    113  * qst:
    114  * Do a quicksort
    115  * First, find the median element, and put that one in the first place as the
    116  * discriminator.  (This "median" is just the median of the first, last and
    117  * middle elements).  (Using this median instead of the first element is a big
    118  * win).  Then, the usual partitioning/swapping, followed by moving the
    119  * discriminator into the right place.  Then, figure out the sizes of the two
    120  * partions, do the smaller one recursively and the larger one via a repeat of
    121  * this code.  Stopping when there are less than THRESH elements in a partition
    122  * and cleaning up with an insertion sort (in our caller) is a huge win.
    123  * All data swaps are done in-line, which is space-losing but time-saving.
    124  * (And there are only three places where this is done).
    125  */
    126 
    127 static void
    128 qst(char *base, char *max)
    129 {
    130 	char c, *i, *j, *jj;
    131 	int ii;
    132 	char *mid, *tmp;
    133 	int lo, hi;
    134 
    135 	/*
    136 	 * At the top here, lo is the number of characters of elements in the
    137 	 * current partition.  (Which should be max - base).
    138 	 * Find the median of the first, last, and middle element and make
    139 	 * that the middle element.  Set j to largest of first and middle.
    140 	 * If max is larger than that guy, then it's that guy, else compare
    141 	 * max with loser of first and take larger.  Things are set up to
    142 	 * prefer the middle, then the first in case of ties.
    143 	 */
    144 	lo = max - base;		/* number of elements as chars */
    145 	do	{
    146 		mid = i = base + qsz * ((lo / qsz) >> 1);
    147 		if (lo >= mthresh) {
    148 			j = (qcmp((jj = base), i) > 0 ? jj : i);
    149 			if (qcmp(j, (tmp = max - qsz)) > 0) {
    150 				/* switch to first loser */
    151 				j = (j == jj ? i : jj);
    152 				if (qcmp(j, tmp) < 0)
    153 					j = tmp;
    154 			}
    155 			if (j != i) {
    156 				ii = qsz;
    157 				do	{
    158 					c = *i;
    159 					*i++ = *j;
    160 					*j++ = c;
    161 				} while (--ii);
    162 			}
    163 		}
    164 		/*
    165 		 * Semi-standard quicksort partitioning/swapping
    166 		 */
    167 		for (i = base, j = max - qsz; ; ) {
    168 			while (i < mid && qcmp(i, mid) <= 0)
    169 				i += qsz;
    170 			while (j > mid) {
    171 				if (qcmp(mid, j) <= 0) {
    172 					j -= qsz;
    173 					continue;
    174 				}
    175 				tmp = i + qsz;	/* value of i after swap */
    176 				if (i == mid) {
    177 					/* j <-> mid, new mid is j */
    178 					mid = jj = j;
    179 				} else {
    180 					/* i <-> j */
    181 					jj = j;
    182 					j -= qsz;
    183 				}
    184 				goto swap;
    185 			}
    186 			if (i == mid) {
    187 				break;
    188 			} else {
    189 				/* i <-> mid, new mid is i */
    190 				jj = mid;
    191 				tmp = mid = i;	/* value of i after swap */
    192 				j -= qsz;
    193 			}
    194 		swap:
    195 			ii = qsz;
    196 			do	{
    197 				c = *i;
    198 				*i++ = *jj;
    199 				*jj++ = c;
    200 			} while (--ii);
    201 			i = tmp;
    202 		}
    203 		/*
    204 		 * Look at sizes of the two partitions, do the smaller
    205 		 * one first by recursion, then do the larger one by
    206 		 * making sure lo is its size, base and max are update
    207 		 * correctly, and branching back.  But only repeat
    208 		 * (recursively or by branching) if the partition is
    209 		 * of at least size THRESH.
    210 		 */
    211 		i = (j = mid) + qsz;
    212 		if ((lo = j - base) <= (hi = max - i)) {
    213 			if (lo >= thresh)
    214 				qst(base, j);
    215 			base = i;
    216 			lo = hi;
    217 		} else {
    218 			if (hi >= thresh)
    219 				qst(i, max);
    220 			max = j;
    221 		}
    222 	} while (lo >= thresh);
    223 }
    224