Branch data Line data Source code
1 : : /*
2 : : * bsearch_arg.c: bsearch variant with a user-supplied pointer
3 : : *
4 : : * Copyright (c) 2021-2026, 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 [rescinded 22 July 1999]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 : 2906196 : 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 : 2906196 : const char *base = (const char *) base0;
61 : 2906196 : size_t lim;
62 : 2906196 : int cmp;
63 : 2906196 : const void *p;
64 : :
65 [ + + ]: 17477078 : for (lim = nmemb; lim != 0; lim >>= 1)
66 : : {
67 : 14579851 : p = base + (lim >> 1) * size;
68 : 14579851 : cmp = (*compar) (key, p, arg);
69 [ + + ]: 14579851 : if (cmp == 0)
70 : 8969 : return (void *) p;
71 [ + + ]: 14570882 : if (cmp > 0)
72 : : { /* key > p: move right */
73 : 14346135 : base = (const char *) p + size;
74 : 14346135 : lim--;
75 : 14346135 : } /* else move left */
76 : 14570882 : }
77 : 2897227 : return (NULL);
78 : 2906196 : }
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