1 | // Copyright (C) 2019 The Qt Company Ltd. |
2 | // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only |
3 | |
4 | #ifndef QPRIMEFORNUMBITS_P_H |
5 | #define QPRIMEFORNUMBITS_P_H |
6 | |
7 | // |
8 | // W A R N I N G |
9 | // ------------- |
10 | // |
11 | // This file is not part of the Qt API. It exists purely as an |
12 | // implementation detail. This header file may change from version to |
13 | // version without notice, or even be removed. |
14 | // |
15 | // We mean it. |
16 | // |
17 | |
18 | #include <private/qtqmlglobal_p.h> |
19 | |
20 | QT_BEGIN_NAMESPACE |
21 | |
22 | /* |
23 | The prime_deltas array is a table of selected prime values, even |
24 | though it doesn't look like one. The primes we are using are 1, |
25 | 2, 5, 11, 17, 37, 67, 131, 257, ..., i.e. primes in the immediate |
26 | surrounding of a power of two. |
27 | |
28 | The qPrimeForNumBits() function returns the prime associated to a |
29 | power of two. For example, qPrimeForNumBits(8) returns 257. |
30 | */ |
31 | |
32 | inline int qPrimeForNumBits(int numBits) |
33 | { |
34 | static constexpr const uchar prime_deltas[] = { |
35 | 0, 0, 1, 3, 1, 5, 3, 3, 1, 9, 7, 5, 3, 9, 25, 3, |
36 | 1, 21, 3, 21, 7, 15, 9, 5, 3, 29, 15, 0, 0, 0, 0, 0 |
37 | }; |
38 | |
39 | return (1 << numBits) + prime_deltas[numBits]; |
40 | } |
41 | |
42 | QT_END_NAMESPACE |
43 | |
44 | #endif // QPRIMEFORNUMBITS_P_H |
45 | |