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Diffstat (limited to 'src/qml/qml/ftw/qprimefornumbits_p.h')
| -rw-r--r-- | src/qml/qml/ftw/qprimefornumbits_p.h | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/src/qml/qml/ftw/qprimefornumbits_p.h b/src/qml/qml/ftw/qprimefornumbits_p.h new file mode 100644 index 0000000000..82c9ea023e --- /dev/null +++ b/src/qml/qml/ftw/qprimefornumbits_p.h @@ -0,0 +1,44 @@ +// Copyright (C) 2019 The Qt Company Ltd. +// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only + +#ifndef QPRIMEFORNUMBITS_P_H +#define QPRIMEFORNUMBITS_P_H + +// +// W A R N I N G +// ------------- +// +// This file is not part of the Qt API. It exists purely as an +// implementation detail. This header file may change from version to +// version without notice, or even be removed. +// +// We mean it. +// + +#include <private/qtqmlglobal_p.h> + +QT_BEGIN_NAMESPACE + +/* + The prime_deltas array is a table of selected prime values, even + though it doesn't look like one. The primes we are using are 1, + 2, 5, 11, 17, 37, 67, 131, 257, ..., i.e. primes in the immediate + surrounding of a power of two. + + The qPrimeForNumBits() function returns the prime associated to a + power of two. For example, qPrimeForNumBits(8) returns 257. +*/ + +inline int qPrimeForNumBits(int numBits) +{ + static constexpr const uchar prime_deltas[] = { + 0, 0, 1, 3, 1, 5, 3, 3, 1, 9, 7, 5, 3, 9, 25, 3, + 1, 21, 3, 21, 7, 15, 9, 5, 3, 29, 15, 0, 0, 0, 0, 0 + }; + + return (1 << numBits) + prime_deltas[numBits]; +} + +QT_END_NAMESPACE + +#endif // QPRIMEFORNUMBITS_P_H |