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1 | /* |
2 | * Copyright (c) 1990 Regents of the University of California. | |
3 | * All rights reserved. | |
4 | * | |
5 | * Redistribution and use in source and binary forms, with or without | |
6 | * modification, are permitted provided that the following conditions | |
7 | * are met: | |
8 | * 1. Redistributions of source code must retain the above copyright | |
9 | * notice, this list of conditions and the following disclaimer. | |
10 | * 2. Redistributions in binary form must reproduce the above copyright | |
11 | * notice, this list of conditions and the following disclaimer in the | |
12 | * documentation and/or other materials provided with the distribution. | |
13 | * 3. [rescinded 22 July 1999] | |
14 | * 4. Neither the name of the University nor the names of its contributors | |
15 | * may be used to endorse or promote products derived from this software | |
16 | * without specific prior written permission. | |
17 | * | |
18 | * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
19 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
20 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
21 | * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |
22 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
23 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
24 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
25 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
26 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |
27 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
28 | * SUCH DAMAGE. | |
29 | */ | |
30 | ||
31 | /* | |
32 | ||
33 | @deftypefn Supplemental void* bsearch_r (const void *@var{key}, @ | |
34 | const void *@var{base}, size_t @var{nmemb}, size_t @var{size}, @ | |
35 | int (*@var{compar})(const void *, const void *, void *), void *@var{arg}) | |
36 | ||
37 | Performs a search over an array of @var{nmemb} elements pointed to by | |
38 | @var{base} for a member that matches the object pointed to by @var{key}. | |
39 | The size of each member is specified by @var{size}. The array contents | |
40 | should be sorted in ascending order according to the @var{compar} | |
41 | comparison function. This routine should take three arguments: the first | |
42 | two point to the @var{key} and to an array member, and the last is passed | |
43 | down unchanged from @code{bsearch_r}'s last argument. It should return an | |
44 | integer less than, equal to, or greater than zero if the @var{key} object | |
45 | is respectively less than, matching, or greater than the array member. | |
46 | ||
47 | @end deftypefn | |
48 | ||
49 | */ | |
50 | ||
51 | #include "config.h" | |
52 | #include "ansidecl.h" | |
53 | #include <sys/types.h> /* size_t */ | |
54 | #include <stdio.h> | |
55 | ||
56 | /* | |
57 | * Perform a binary search. | |
58 | * | |
59 | * The code below is a bit sneaky. After a comparison fails, we | |
60 | * divide the work in half by moving either left or right. If lim | |
61 | * is odd, moving left simply involves halving lim: e.g., when lim | |
62 | * is 5 we look at item 2, so we change lim to 2 so that we will | |
63 | * look at items 0 & 1. If lim is even, the same applies. If lim | |
64 | * is odd, moving right again involes halving lim, this time moving | |
65 | * the base up one item past p: e.g., when lim is 5 we change base | |
66 | * to item 3 and make lim 2 so that we will look at items 3 and 4. | |
67 | * If lim is even, however, we have to shrink it by one before | |
68 | * halving: e.g., when lim is 4, we still looked at item 2, so we | |
69 | * have to make lim 3, then halve, obtaining 1, so that we will only | |
70 | * look at item 3. | |
71 | */ | |
72 | void * | |
73 | bsearch_r (register const void *key, const void *base0, | |
74 | size_t nmemb, register size_t size, | |
75 | register int (*compar)(const void *, const void *, void *), | |
76 | void *arg) | |
77 | { | |
78 | register const char *base = (const char *) base0; | |
79 | register int lim, cmp; | |
80 | register const void *p; | |
81 | ||
82 | for (lim = nmemb; lim != 0; lim >>= 1) { | |
83 | p = base + (lim >> 1) * size; | |
84 | cmp = (*compar)(key, p, arg); | |
85 | if (cmp == 0) | |
86 | return (void *)p; | |
87 | if (cmp > 0) { /* key > p: move right */ | |
88 | base = (const char *)p + size; | |
89 | lim--; | |
90 | } /* else move left */ | |
91 | } | |
92 | return (NULL); | |
93 | } |