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qsort_arg.c
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1 /*
2  * qsort_arg.c: qsort with a passthrough "void *" argument
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.c, gen_qsort_tuple.pl
12  *
13  * src/port/qsort_arg.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 
50 static char *med3(char *a, char *b, char *c,
52 static 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) \
71 do { \
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 
85 static void
86 swapfunc(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 
104 static char *
105 med3(char *a, char *b, char *c, qsort_arg_comparator cmp, void *arg)
106 {
107  return cmp(a, b, arg) < 0 ?
108  (cmp(b, c, arg) < 0 ? b : (cmp(a, c, arg) < 0 ? c : a))
109  : (cmp(b, c, arg) > 0 ? b : (cmp(a, c, arg) < 0 ? a : c));
110 }
111 
112 void
113 qsort_arg(void *a, size_t n, size_t es, qsort_arg_comparator cmp, void *arg)
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 
128 loop: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, arg) > 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, arg) > 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, arg);
158  pm = med3(pm - d, pm, pm + d, cmp, arg);
159  pn = med3(pn - 2 * d, pn - d, pn, cmp, arg);
160  }
161  pm = med3(pl, pm, pn, cmp, arg);
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, arg)) <= 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, arg)) >= 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  qsort_arg(a, d1 / es, es, cmp, arg);
204  if (d2 > es)
205  {
206  /* Iterate rather than recurse to save stack space */
207  /* qsort_arg(pn - d2, d2 / es, es, cmp, arg); */
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  qsort_arg(pn - d2, d2 / es, es, cmp, arg);
218  if (d1 > es)
219  {
220  /* Iterate rather than recurse to save stack space */
221  /* qsort_arg(a, d1 / es, es, cmp, arg); */
222  n = d1 / es;
223  goto loop;
224  }
225  }
226 }
int(* qsort_arg_comparator)(const void *a, const void *b, void *arg)
Definition: port.h:410
#define Min(x, y)
Definition: c.h:802
void qsort_arg(void *a, size_t n, size_t es, qsort_arg_comparator cmp, void *arg)
Definition: qsort_arg.c:113
#define SWAPINIT(a, es)
Definition: qsort_arg.c:82
static char * med3(char *a, char *b, char *c, qsort_arg_comparator cmp, void *arg)
Definition: qsort_arg.c:105
static void swapfunc(char *, char *, size_t, int)
Definition: qsort_arg.c:86
char * c
#define vecswap(a, b, n)
Definition: qsort_arg.c:102
#define swapcode(TYPE, parmi, parmj, n)
Definition: qsort_arg.c:70
#define swap(a, b)
Definition: qsort_arg.c:94
void * arg
static int cmp(const chr *x, const chr *y, size_t len)
Definition: regc_locale.c:742