xref: /freebsd/lib/libc/stdlib/qsort.c (revision c1d255d3ffdbe447de3ab875bf4e7d7accc5bfc5)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 1992, 1993
5  *	The Regents of the University of California.  All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  * 2. Redistributions in binary form must reproduce the above copyright
13  *    notice, this list of conditions and the following disclaimer in the
14  *    documentation and/or other materials provided with the distribution.
15  * 3. Neither the name of the University nor the names of its contributors
16  *    may be used to endorse or promote products derived from this software
17  *    without specific prior written permission.
18  *
19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29  * SUCH DAMAGE.
30  */
31 
32 #if defined(LIBC_SCCS) && !defined(lint)
33 static char sccsid[] = "@(#)qsort.c	8.1 (Berkeley) 6/4/93";
34 #endif /* LIBC_SCCS and not lint */
35 #include <sys/cdefs.h>
36 __FBSDID("$FreeBSD$");
37 
38 #include <errno.h>
39 #include <stdint.h>
40 #include <stdlib.h>
41 #include <string.h>
42 #include "libc_private.h"
43 
44 #if defined(I_AM_QSORT_R)
45 typedef int		 cmp_t(void *, const void *, const void *);
46 #elif defined(I_AM_QSORT_S)
47 typedef int		 cmp_t(const void *, const void *, void *);
48 #else
49 typedef int		 cmp_t(const void *, const void *);
50 #endif
51 static inline char	*med3(char *, char *, char *, cmp_t *, void *);
52 
53 #define	MIN(a, b)	((a) < (b) ? a : b)
54 
55 /*
56  * Qsort routine from Bentley & McIlroy's "Engineering a Sort Function".
57  */
58 
59 static inline void
60 swapfunc(char *a, char *b, size_t es)
61 {
62 	char t;
63 
64 	do {
65 		t = *a;
66 		*a++ = *b;
67 		*b++ = t;
68 	} while (--es > 0);
69 }
70 
71 #define	vecswap(a, b, n)				\
72 	if ((n) > 0) swapfunc(a, b, n)
73 
74 #if defined(I_AM_QSORT_R)
75 #define	CMP(t, x, y) (cmp((t), (x), (y)))
76 #elif defined(I_AM_QSORT_S)
77 #define	CMP(t, x, y) (cmp((x), (y), (t)))
78 #else
79 #define	CMP(t, x, y) (cmp((x), (y)))
80 #endif
81 
82 static inline char *
83 med3(char *a, char *b, char *c, cmp_t *cmp, void *thunk
84 #if !defined(I_AM_QSORT_R) && !defined(I_AM_QSORT_S)
85 __unused
86 #endif
87 )
88 {
89 	return CMP(thunk, a, b) < 0 ?
90 	       (CMP(thunk, b, c) < 0 ? b : (CMP(thunk, a, c) < 0 ? c : a ))
91 	      :(CMP(thunk, b, c) > 0 ? b : (CMP(thunk, a, c) < 0 ? a : c ));
92 }
93 
94 /*
95  * The actual qsort() implementation is static to avoid preemptible calls when
96  * recursing. Also give them different names for improved debugging.
97  */
98 #if defined(I_AM_QSORT_R)
99 #define local_qsort local_qsort_r
100 #elif defined(I_AM_QSORT_S)
101 #define local_qsort local_qsort_s
102 #endif
103 static void
104 local_qsort(void *a, size_t n, size_t es, cmp_t *cmp, void *thunk)
105 {
106 	char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
107 	size_t d1, d2;
108 	int cmp_result;
109 	int swap_cnt;
110 
111 loop:
112 	swap_cnt = 0;
113 	if (n < 7) {
114 		for (pm = (char *)a + es; pm < (char *)a + n * es; pm += es)
115 			for (pl = pm;
116 			     pl > (char *)a && CMP(thunk, pl - es, pl) > 0;
117 			     pl -= es)
118 				swapfunc(pl, pl - es, es);
119 		return;
120 	}
121 	pm = (char *)a + (n / 2) * es;
122 	if (n > 7) {
123 		pl = a;
124 		pn = (char *)a + (n - 1) * es;
125 		if (n > 40) {
126 			size_t d = (n / 8) * es;
127 
128 			pl = med3(pl, pl + d, pl + 2 * d, cmp, thunk);
129 			pm = med3(pm - d, pm, pm + d, cmp, thunk);
130 			pn = med3(pn - 2 * d, pn - d, pn, cmp, thunk);
131 		}
132 		pm = med3(pl, pm, pn, cmp, thunk);
133 	}
134 	swapfunc(a, pm, es);
135 	pa = pb = (char *)a + es;
136 
137 	pc = pd = (char *)a + (n - 1) * es;
138 	for (;;) {
139 		while (pb <= pc && (cmp_result = CMP(thunk, pb, a)) <= 0) {
140 			if (cmp_result == 0) {
141 				swap_cnt = 1;
142 				swapfunc(pa, pb, es);
143 				pa += es;
144 			}
145 			pb += es;
146 		}
147 		while (pb <= pc && (cmp_result = CMP(thunk, pc, a)) >= 0) {
148 			if (cmp_result == 0) {
149 				swap_cnt = 1;
150 				swapfunc(pc, pd, es);
151 				pd -= es;
152 			}
153 			pc -= es;
154 		}
155 		if (pb > pc)
156 			break;
157 		swapfunc(pb, pc, es);
158 		swap_cnt = 1;
159 		pb += es;
160 		pc -= es;
161 	}
162 	if (swap_cnt == 0) {  /* Switch to insertion sort */
163 		for (pm = (char *)a + es; pm < (char *)a + n * es; pm += es)
164 			for (pl = pm;
165 			     pl > (char *)a && CMP(thunk, pl - es, pl) > 0;
166 			     pl -= es)
167 				swapfunc(pl, pl - es, es);
168 		return;
169 	}
170 
171 	pn = (char *)a + n * es;
172 	d1 = MIN(pa - (char *)a, pb - pa);
173 	vecswap(a, pb - d1, d1);
174 	/*
175 	 * Cast es to preserve signedness of right-hand side of MIN()
176 	 * expression, to avoid sign ambiguity in the implied comparison.  es
177 	 * is safely within [0, SSIZE_MAX].
178 	 */
179 	d1 = MIN(pd - pc, pn - pd - (ssize_t)es);
180 	vecswap(pb, pn - d1, d1);
181 
182 	d1 = pb - pa;
183 	d2 = pd - pc;
184 	if (d1 <= d2) {
185 		/* Recurse on left partition, then iterate on right partition */
186 		if (d1 > es) {
187 			local_qsort(a, d1 / es, es, cmp, thunk);
188 		}
189 		if (d2 > es) {
190 			/* Iterate rather than recurse to save stack space */
191 			/* qsort(pn - d2, d2 / es, es, cmp); */
192 			a = pn - d2;
193 			n = d2 / es;
194 			goto loop;
195 		}
196 	} else {
197 		/* Recurse on right partition, then iterate on left partition */
198 		if (d2 > es) {
199 			local_qsort(pn - d2, d2 / es, es, cmp, thunk);
200 		}
201 		if (d1 > es) {
202 			/* Iterate rather than recurse to save stack space */
203 			/* qsort(a, d1 / es, es, cmp); */
204 			n = d1 / es;
205 			goto loop;
206 		}
207 	}
208 }
209 
210 #if defined(I_AM_QSORT_R)
211 void
212 qsort_r(void *a, size_t n, size_t es, void *thunk, cmp_t *cmp)
213 {
214 	local_qsort_r(a, n, es, cmp, thunk);
215 }
216 #elif defined(I_AM_QSORT_S)
217 errno_t
218 qsort_s(void *a, rsize_t n, rsize_t es, cmp_t *cmp, void *thunk)
219 {
220 	if (n > RSIZE_MAX) {
221 		__throw_constraint_handler_s("qsort_s : n > RSIZE_MAX", EINVAL);
222 		return (EINVAL);
223 	} else if (es > RSIZE_MAX) {
224 		__throw_constraint_handler_s("qsort_s : es > RSIZE_MAX",
225 		    EINVAL);
226 		return (EINVAL);
227 	} else if (n != 0) {
228 		if (a == NULL) {
229 			__throw_constraint_handler_s("qsort_s : a == NULL",
230 			    EINVAL);
231 			return (EINVAL);
232 		} else if (cmp == NULL) {
233 			__throw_constraint_handler_s("qsort_s : cmp == NULL",
234 			    EINVAL);
235 			return (EINVAL);
236 		}
237 	}
238 
239 	local_qsort_s(a, n, es, cmp, thunk);
240 	return (0);
241 }
242 #else
243 void
244 qsort(void *a, size_t n, size_t es, cmp_t *cmp)
245 {
246 	local_qsort(a, n, es, cmp, NULL);
247 }
248 #endif
249