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39
40#ifndef QPRIMEFORNUMBITS_P_H
41#define QPRIMEFORNUMBITS_P_H
42
43//
44// W A R N I N G
45// -------------
46//
47// This file is not part of the Qt API. It exists purely as an
48// implementation detail. This header file may change from version to
49// version without notice, or even be removed.
50//
51// We mean it.
52//
53
54#include <private/qtqmlglobal_p.h>
55
56QT_BEGIN_NAMESPACE
57
58/*
59 The prime_deltas array is a table of selected prime values, even
60 though it doesn't look like one. The primes we are using are 1,
61 2, 5, 11, 17, 37, 67, 131, 257, ..., i.e. primes in the immediate
62 surrounding of a power of two.
63
64 The qPrimeForNumBits() function returns the prime associated to a
65 power of two. For example, qPrimeForNumBits(8) returns 257.
66*/
67
68inline int qPrimeForNumBits(int numBits)
69{
70 static constexpr const uchar prime_deltas[] = {
71 0, 0, 1, 3, 1, 5, 3, 3, 1, 9, 7, 5, 3, 9, 25, 3,
72 1, 21, 3, 21, 7, 15, 9, 5, 3, 29, 15, 0, 0, 0, 0, 0
73 };
74
75 return (1 << numBits) + prime_deltas[numBits];
76}
77
78QT_END_NAMESPACE
79
80#endif // QPRIMEFORNUMBITS_P_H
81

source code of qtdeclarative/src/qml/qml/ftw/qprimefornumbits_p.h