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bsearch_arg.c
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1 /*
2  * bsearch_arg.c: bsearch variant with a user-supplied pointer
3  *
4  * Copyright (c) 2021, PostgreSQL Global Development Group
5  * Copyright (c) 1990 Regents of the University of California.
6  * All rights reserved.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  * notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  * notice, this list of conditions and the following disclaimer in the
15  * documentation and/or other materials provided with the distribution.
16  * 3. [rescinded 22 July 1999]
17  * 4. Neither the name of the University nor the names of its contributors
18  * may be used to endorse or promote products derived from this software
19  * without specific prior written permission.
20  *
21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24  * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  *
33  * src/port/bsearch_arg.c
34  */
35 
36 #include "c.h"
37 
38 /*
39  * Perform a binary search.
40  *
41  * The code below is a bit sneaky. After a comparison fails, we
42  * divide the work in half by moving either left or right. If lim
43  * is odd, moving left simply involves halving lim: e.g., when lim
44  * is 5 we look at item 2, so we change lim to 2 so that we will
45  * look at items 0 & 1. If lim is even, the same applies. If lim
46  * is odd, moving right again involves halving lim, this time moving
47  * the base up one item past p: e.g., when lim is 5 we change base
48  * to item 3 and make lim 2 so that we will look at items 3 and 4.
49  * If lim is even, however, we have to shrink it by one before
50  * halving: e.g., when lim is 4, we still looked at item 2, so we
51  * have to make lim 3, then halve, obtaining 1, so that we will only
52  * look at item 3.
53  */
54 void *
55 bsearch_arg(const void *key, const void *base0,
56  size_t nmemb, size_t size,
57  int (*compar) (const void *, const void *, void *),
58  void *arg)
59 {
60  const char *base = (const char *) base0;
61  int lim,
62  cmp;
63  const void *p;
64 
65  for (lim = nmemb; lim != 0; lim >>= 1)
66  {
67  p = base + (lim >> 1) * size;
68  cmp = (*compar) (key, p, arg);
69  if (cmp == 0)
70  return (void *) p;
71  if (cmp > 0)
72  { /* key > p: move right */
73  base = (const char *) p + size;
74  lim--;
75  } /* else move left */
76  }
77  return (NULL);
78 }
void * bsearch_arg(const void *key, const void *base0, size_t nmemb, size_t size, int(*compar)(const void *, const void *, void *), void *arg)
Definition: bsearch_arg.c:55
void * arg
static int cmp(const chr *x, const chr *y, size_t len)
Definition: regc_locale.c:747