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1.1 root 1: /*
2: * Copyright (c) 1980 Regents of the University of California.
3: * All rights reserved.
4: *
5: * Redistribution and use in source and binary forms are permitted
6: * provided that the above copyright notice and this paragraph are
7: * duplicated in all such forms and that any documentation,
8: * advertising materials, and other materials related to such
9: * distribution and use acknowledge that the software was developed
10: * by the University of California, Berkeley. The name of the
11: * University may not be used to endorse or promote products derived
12: * from this software without specific prior written permission.
13: * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
14: * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
15: * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
16: */
17:
18: #if defined(LIBC_SCCS) && !defined(lint)
19: static char sccsid[] = "@(#)qsort.c 5.4 (Berkeley) 6/27/88";
20: #endif /* LIBC_SCCS and not lint */
21:
22: /*
23: * qsort.c:
24: * Our own version of the system qsort routine which is faster by an average
25: * of 25%, with lows and highs of 10% and 50%.
26: * The THRESHold below is the insertion sort threshold, and has been adjusted
27: * for records of size 48 bytes.
28: * The MTHREShold is where we stop finding a better median.
29: */
30:
31: #define THRESH 4 /* threshold for insertion */
32: #define MTHRESH 6 /* threshold for median */
33:
34: static int (*qcmp)(); /* the comparison routine */
35: static int qsz; /* size of each record */
36: static int thresh; /* THRESHold in chars */
37: static int mthresh; /* MTHRESHold in chars */
38:
39: /*
40: * qsort:
41: * First, set up some global parameters for qst to share. Then, quicksort
42: * with qst(), and then a cleanup insertion sort ourselves. Sound simple?
43: * It's not...
44: */
45:
46: qsort(base, n, size, compar)
47: char *base;
48: int n;
49: int size;
50: int (*compar)();
51: {
52: register char c, *i, *j, *lo, *hi;
53: char *min, *max;
54:
55: if (n <= 1)
56: return;
57: qsz = size;
58: qcmp = compar;
59: thresh = qsz * THRESH;
60: mthresh = qsz * MTHRESH;
61: max = base + n * qsz;
62: if (n >= THRESH) {
63: qst(base, max);
64: hi = base + thresh;
65: } else {
66: hi = max;
67: }
68: /*
69: * First put smallest element, which must be in the first THRESH, in
70: * the first position as a sentinel. This is done just by searching
71: * the first THRESH elements (or the first n if n < THRESH), finding
72: * the min, and swapping it into the first position.
73: */
74: for (j = lo = base; (lo += qsz) < hi; )
75: if (qcmp(j, lo) > 0)
76: j = lo;
77: if (j != base) {
78: /* swap j into place */
79: for (i = base, hi = base + qsz; i < hi; ) {
80: c = *j;
81: *j++ = *i;
82: *i++ = c;
83: }
84: }
85: /*
86: * With our sentinel in place, we now run the following hyper-fast
87: * insertion sort. For each remaining element, min, from [1] to [n-1],
88: * set hi to the index of the element AFTER which this one goes.
89: * Then, do the standard insertion sort shift on a character at a time
90: * basis for each element in the frob.
91: */
92: for (min = base; (hi = min += qsz) < max; ) {
93: while (qcmp(hi -= qsz, min) > 0)
94: /* void */;
95: if ((hi += qsz) != min) {
96: for (lo = min + qsz; --lo >= min; ) {
97: c = *lo;
98: for (i = j = lo; (j -= qsz) >= hi; i = j)
99: *i = *j;
100: *i = c;
101: }
102: }
103: }
104: }
105:
106: /*
107: * qst:
108: * Do a quicksort
109: * First, find the median element, and put that one in the first place as the
110: * discriminator. (This "median" is just the median of the first, last and
111: * middle elements). (Using this median instead of the first element is a big
112: * win). Then, the usual partitioning/swapping, followed by moving the
113: * discriminator into the right place. Then, figure out the sizes of the two
114: * partions, do the smaller one recursively and the larger one via a repeat of
115: * this code. Stopping when there are less than THRESH elements in a partition
116: * and cleaning up with an insertion sort (in our caller) is a huge win.
117: * All data swaps are done in-line, which is space-losing but time-saving.
118: * (And there are only three places where this is done).
119: */
120:
121: static
122: qst(base, max)
123: char *base, *max;
124: {
125: register char c, *i, *j, *jj;
126: register int ii;
127: char *mid, *tmp;
128: int lo, hi;
129:
130: /*
131: * At the top here, lo is the number of characters of elements in the
132: * current partition. (Which should be max - base).
133: * Find the median of the first, last, and middle element and make
134: * that the middle element. Set j to largest of first and middle.
135: * If max is larger than that guy, then it's that guy, else compare
136: * max with loser of first and take larger. Things are set up to
137: * prefer the middle, then the first in case of ties.
138: */
139: lo = max - base; /* number of elements as chars */
140: do {
141: mid = i = base + qsz * ((lo / qsz) >> 1);
142: if (lo >= mthresh) {
143: j = (qcmp((jj = base), i) > 0 ? jj : i);
144: if (qcmp(j, (tmp = max - qsz)) > 0) {
145: /* switch to first loser */
146: j = (j == jj ? i : jj);
147: if (qcmp(j, tmp) < 0)
148: j = tmp;
149: }
150: if (j != i) {
151: ii = qsz;
152: do {
153: c = *i;
154: *i++ = *j;
155: *j++ = c;
156: } while (--ii);
157: }
158: }
159: /*
160: * Semi-standard quicksort partitioning/swapping
161: */
162: for (i = base, j = max - qsz; ; ) {
163: while (i < mid && qcmp(i, mid) <= 0)
164: i += qsz;
165: while (j > mid) {
166: if (qcmp(mid, j) <= 0) {
167: j -= qsz;
168: continue;
169: }
170: tmp = i + qsz; /* value of i after swap */
171: if (i == mid) {
172: /* j <-> mid, new mid is j */
173: mid = jj = j;
174: } else {
175: /* i <-> j */
176: jj = j;
177: j -= qsz;
178: }
179: goto swap;
180: }
181: if (i == mid) {
182: break;
183: } else {
184: /* i <-> mid, new mid is i */
185: jj = mid;
186: tmp = mid = i; /* value of i after swap */
187: j -= qsz;
188: }
189: swap:
190: ii = qsz;
191: do {
192: c = *i;
193: *i++ = *jj;
194: *jj++ = c;
195: } while (--ii);
196: i = tmp;
197: }
198: /*
199: * Look at sizes of the two partitions, do the smaller
200: * one first by recursion, then do the larger one by
201: * making sure lo is its size, base and max are update
202: * correctly, and branching back. But only repeat
203: * (recursively or by branching) if the partition is
204: * of at least size THRESH.
205: */
206: i = (j = mid) + qsz;
207: if ((lo = j - base) <= (hi = max - i)) {
208: if (lo >= thresh)
209: qst(base, j);
210: base = i;
211: lo = hi;
212: } else {
213: if (hi >= thresh)
214: qst(i, max);
215: max = j;
216: }
217: } while (lo >= thresh);
218: }
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