1/*
2 * qsort.c: standard quicksort algorithm
3 *
4 * Modifications from vanilla NetBSD source:
5 * Add do ... while() macro fix
6 * Remove __inline, _DIAGASSERTs, __P
7 * Remove ill-considered "swap_cnt" switch to insertion sort,
8 * in favor of a simple check for presorted input.
9 * Take care to recurse on the smaller partition, to bound stack usage.
10 *
11 * CAUTION: if you change this file, see also qsort_arg.c, gen_qsort_tuple.pl
12 *
13 * src/port/qsort.c
14 */
15
16/* $NetBSD: qsort.c,v 1.13 2003/08/07 16:43:42 agc Exp $ */
17
18/*-
19 * Copyright (c) 1992, 1993
20 * The Regents of the University of California. All rights reserved.
21 *
22 * Redistribution and use in source and binary forms, with or without
23 * modification, are permitted provided that the following conditions
24 * are met:
25 * 1. Redistributions of source code must retain the above copyright
26 * notice, this list of conditions and the following disclaimer.
27 * 2. Redistributions in binary form must reproduce the above copyright
28 * notice, this list of conditions and the following disclaimer in the
29 * documentation and/or other materials provided with the distribution.
30 * 3. Neither the name of the University nor the names of its contributors
31 * may be used to endorse or promote products derived from this software
32 * without specific prior written permission.
33 *
34 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
35 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
36 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
37 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
38 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
39 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
40 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
41 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
42 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
43 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
44 * SUCH DAMAGE.
45 */
46
47#include "c.h"
48
49
50static char *med3(char *a, char *b, char *c,
51 int (*cmp) (const void *, const void *));
52static void swapfunc(char *, char *, size_t, int);
53
54/*
55 * Qsort routine based on J. L. Bentley and M. D. McIlroy,
56 * "Engineering a sort function",
57 * Software--Practice and Experience 23 (1993) 1249-1265.
58 *
59 * We have modified their original by adding a check for already-sorted input,
60 * which seems to be a win per discussions on pgsql-hackers around 2006-03-21.
61 *
62 * Also, we recurse on the smaller partition and iterate on the larger one,
63 * which ensures we cannot recurse more than log(N) levels (since the
64 * partition recursed to is surely no more than half of the input). Bentley
65 * and McIlroy explicitly rejected doing this on the grounds that it's "not
66 * worth the effort", but we have seen crashes in the field due to stack
67 * overrun, so that judgment seems wrong.
68 */
69
70#define swapcode(TYPE, parmi, parmj, n) \
71do { \
72 size_t i = (n) / sizeof (TYPE); \
73 TYPE *pi = (TYPE *)(void *)(parmi); \
74 TYPE *pj = (TYPE *)(void *)(parmj); \
75 do { \
76 TYPE t = *pi; \
77 *pi++ = *pj; \
78 *pj++ = t; \
79 } while (--i > 0); \
80} while (0)
81
82#define SWAPINIT(a, es) swaptype = ((char *)(a) - (char *)0) % sizeof(long) || \
83 (es) % sizeof(long) ? 2 : (es) == sizeof(long)? 0 : 1;
84
85static void
86swapfunc(char *a, char *b, size_t n, int swaptype)
87{
88 if (swaptype <= 1)
89 swapcode(long, a, b, n);
90 else
91 swapcode(char, a, b, n);
92}
93
94#define swap(a, b) \
95 if (swaptype == 0) { \
96 long t = *(long *)(void *)(a); \
97 *(long *)(void *)(a) = *(long *)(void *)(b); \
98 *(long *)(void *)(b) = t; \
99 } else \
100 swapfunc(a, b, es, swaptype)
101
102#define vecswap(a, b, n) if ((n) > 0) swapfunc(a, b, n, swaptype)
103
104static char *
105med3(char *a, char *b, char *c, int (*cmp) (const void *, const void *))
106{
107 return cmp(a, b) < 0 ?
108 (cmp(b, c) < 0 ? b : (cmp(a, c) < 0 ? c : a))
109 : (cmp(b, c) > 0 ? b : (cmp(a, c) < 0 ? a : c));
110}
111
112void
113pg_qsort(void *a, size_t n, size_t es, int (*cmp) (const void *, const void *))
114{
115 char *pa,
116 *pb,
117 *pc,
118 *pd,
119 *pl,
120 *pm,
121 *pn;
122 size_t d1,
123 d2;
124 int r,
125 swaptype,
126 presorted;
127
128loop:SWAPINIT(a, es);
129 if (n < 7)
130 {
131 for (pm = (char *) a + es; pm < (char *) a + n * es; pm += es)
132 for (pl = pm; pl > (char *) a && cmp(pl - es, pl) > 0;
133 pl -= es)
134 swap(pl, pl - es);
135 return;
136 }
137 presorted = 1;
138 for (pm = (char *) a + es; pm < (char *) a + n * es; pm += es)
139 {
140 if (cmp(pm - es, pm) > 0)
141 {
142 presorted = 0;
143 break;
144 }
145 }
146 if (presorted)
147 return;
148 pm = (char *) a + (n / 2) * es;
149 if (n > 7)
150 {
151 pl = (char *) a;
152 pn = (char *) a + (n - 1) * es;
153 if (n > 40)
154 {
155 size_t d = (n / 8) * es;
156
157 pl = med3(pl, pl + d, pl + 2 * d, cmp);
158 pm = med3(pm - d, pm, pm + d, cmp);
159 pn = med3(pn - 2 * d, pn - d, pn, cmp);
160 }
161 pm = med3(pl, pm, pn, cmp);
162 }
163 swap(a, pm);
164 pa = pb = (char *) a + es;
165 pc = pd = (char *) a + (n - 1) * es;
166 for (;;)
167 {
168 while (pb <= pc && (r = cmp(pb, a)) <= 0)
169 {
170 if (r == 0)
171 {
172 swap(pa, pb);
173 pa += es;
174 }
175 pb += es;
176 }
177 while (pb <= pc && (r = cmp(pc, a)) >= 0)
178 {
179 if (r == 0)
180 {
181 swap(pc, pd);
182 pd -= es;
183 }
184 pc -= es;
185 }
186 if (pb > pc)
187 break;
188 swap(pb, pc);
189 pb += es;
190 pc -= es;
191 }
192 pn = (char *) a + n * es;
193 d1 = Min(pa - (char *) a, pb - pa);
194 vecswap(a, pb - d1, d1);
195 d1 = Min(pd - pc, pn - pd - es);
196 vecswap(pb, pn - d1, d1);
197 d1 = pb - pa;
198 d2 = pd - pc;
199 if (d1 <= d2)
200 {
201 /* Recurse on left partition, then iterate on right partition */
202 if (d1 > es)
203 pg_qsort(a, d1 / es, es, cmp);
204 if (d2 > es)
205 {
206 /* Iterate rather than recurse to save stack space */
207 /* pg_qsort(pn - d2, d2 / es, es, cmp); */
208 a = pn - d2;
209 n = d2 / es;
210 goto loop;
211 }
212 }
213 else
214 {
215 /* Recurse on right partition, then iterate on left partition */
216 if (d2 > es)
217 pg_qsort(pn - d2, d2 / es, es, cmp);
218 if (d1 > es)
219 {
220 /* Iterate rather than recurse to save stack space */
221 /* pg_qsort(a, d1 / es, es, cmp); */
222 n = d1 / es;
223 goto loop;
224 }
225 }
226}
227
228/*
229 * qsort comparator wrapper for strcmp.
230 */
231int
232pg_qsort_strcmp(const void *a, const void *b)
233{
234 return strcmp(*(const char *const *) a, *(const char *const *) b);
235}
236