xref: /onnv-gate/usr/src/lib/libbc/libc/gen/common/qsort.c (revision 722:636b850d4ee9)
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
qsort(char * base,int n,int size,int (* compar)())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
qst(char * base,char * max)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