1 /*
2 * Copyright (c) 2022, The OpenThread Authors.
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 are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 * 3. Neither the name of the copyright holder nor the
13 * names of its contributors may be used to endorse or promote products
14 * derived from this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
17 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
20 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
23 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
24 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
25 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
26 * POSSIBILITY OF SUCH DAMAGE.
27 */
28
29 /**
30 * @file
31 * This file implements a generic binary search.
32 */
33
34 #include "binary_search.hpp"
35
36 #include "common/code_utils.hpp"
37
38 namespace ot {
39
Find(const void * aKey,const void * aTable,uint16_t aLength,uint16_t aEntrySize,Comparator aComparator)40 const void *BinarySearch::Find(const void *aKey,
41 const void *aTable,
42 uint16_t aLength,
43 uint16_t aEntrySize,
44 Comparator aComparator)
45 {
46 const void *entry;
47 uint16_t left = 0;
48 uint16_t right = aLength;
49
50 while (left < right)
51 {
52 uint16_t middle = (left + right) / 2;
53 int compare;
54
55 // Note that `aTable` array entry type is not known here and
56 // only its size is given as `aEntrySize`. Based on this, we
57 // can calculate the pointer to the table entry at any index
58 // (such as `[middle]`) which is then passed to the given
59 // `aComparator` function which knows how to cast the void
60 // pointer to proper entry type and compare it with `aKey`.
61 // This model keeps the implementation generic and reusable
62 // allowing it to be used with any entry type.
63
64 entry = reinterpret_cast<const uint8_t *>(aTable) + aEntrySize * middle;
65
66 compare = aComparator(aKey, entry);
67
68 if (compare == 0)
69 {
70 ExitNow();
71 }
72 else if (compare > 0)
73 {
74 left = middle + 1;
75 }
76 else
77 {
78 right = middle;
79 }
80 }
81
82 entry = nullptr;
83
84 exit:
85 return entry;
86 }
87
88 } // namespace ot
89
