1 | // Copyright (C) 2020 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 QTAGGEDPOINTER_H |
5 | #define QTAGGEDPOINTER_H |
6 | |
7 | #include <QtCore/qglobal.h> |
8 | #include <QtCore/qalgorithms.h> |
9 | #include <QtCore/qmath.h> |
10 | #include <QtCore/qtypeinfo.h> |
11 | |
12 | QT_BEGIN_NAMESPACE |
13 | |
14 | namespace QtPrivate { |
15 | constexpr quint8 nextByteSize(quint8 bits) { return quint8((bits + 7) / 8); } |
16 | |
17 | template <typename T> |
18 | struct TagInfo |
19 | { |
20 | static constexpr size_t alignment = alignof(T); |
21 | static_assert((alignment & (alignment - 1)) == 0, |
22 | "Alignment of template parameter must be power of two" ); |
23 | |
24 | static constexpr quint8 tagBits = quint8{QtPrivate::qConstexprCountTrailingZeroBits(v: alignment)}; |
25 | static_assert(tagBits > 0, |
26 | "Alignment of template parameter does not allow any tags" ); |
27 | |
28 | static constexpr size_t tagSize = QtPrivate::qConstexprNextPowerOfTwo(v: nextByteSize(bits: tagBits)); |
29 | static_assert(tagSize < sizeof(quintptr), |
30 | "Alignment of template parameter allows tags masking away pointer" ); |
31 | |
32 | using TagType = typename QIntegerForSize<tagSize>::Unsigned; |
33 | }; |
34 | } |
35 | |
36 | template <typename T, typename Tag = typename QtPrivate::TagInfo<T>::TagType> |
37 | class QTaggedPointer |
38 | { |
39 | public: |
40 | using Type = T; |
41 | using TagType = Tag; |
42 | |
43 | static constexpr quintptr tagMask() { return QtPrivate::TagInfo<T>::alignment - 1; } |
44 | static constexpr quintptr pointerMask() { return ~tagMask(); } |
45 | |
46 | Q_NODISCARD_CTOR constexpr QTaggedPointer() noexcept : d(0) {} |
47 | Q_NODISCARD_CTOR constexpr QTaggedPointer(std::nullptr_t) noexcept : QTaggedPointer() {} |
48 | |
49 | Q_NODISCARD_CTOR explicit QTaggedPointer(T *pointer, Tag tag = Tag()) noexcept |
50 | : d(quintptr(pointer) | quintptr(tag)) |
51 | { |
52 | static_assert(sizeof(Type*) == sizeof(QTaggedPointer)); |
53 | |
54 | Q_ASSERT_X((quintptr(pointer) & tagMask()) == 0, "QTaggedPointer<T, Tag>" , "Pointer is not aligned" ); |
55 | Q_ASSERT_X((static_cast<typename QtPrivate::TagInfo<T>::TagType>(tag) & pointerMask()) == 0, |
56 | "QTaggedPointer<T, Tag>::setTag" , "Tag is larger than allowed by number of available tag bits" ); |
57 | } |
58 | |
59 | Type &operator*() const noexcept |
60 | { |
61 | Q_ASSERT(data()); |
62 | return *data(); |
63 | } |
64 | |
65 | Type *operator->() const noexcept |
66 | { |
67 | return data(); |
68 | } |
69 | |
70 | explicit operator bool() const noexcept |
71 | { |
72 | return !isNull(); |
73 | } |
74 | |
75 | #ifdef Q_QDOC |
76 | QTaggedPointer &operator=(T *other) noexcept; |
77 | #else |
78 | // Disables the usage of `ptr = {}`, which would go through this operator |
79 | // (rather than using the implicitly-generated assignment operator). |
80 | // The operators have different semantics: the ones here leave the tag intact, |
81 | // the implicitly-generated one overwrites it. |
82 | template <typename U, |
83 | std::enable_if_t<std::is_convertible_v<U *, T *>, bool> = false> |
84 | QTaggedPointer &operator=(U *other) noexcept |
85 | { |
86 | T *otherT = other; |
87 | d = reinterpret_cast<quintptr>(otherT) | (d & tagMask()); |
88 | return *this; |
89 | } |
90 | |
91 | template <typename U, |
92 | std::enable_if_t<std::is_null_pointer_v<U>, bool> = false> |
93 | QTaggedPointer &operator=(U) noexcept |
94 | { |
95 | d = reinterpret_cast<quintptr>(static_cast<T *>(nullptr)) | (d & tagMask()); |
96 | return *this; |
97 | } |
98 | #endif |
99 | |
100 | static constexpr Tag maximumTag() noexcept |
101 | { |
102 | return TagType(typename QtPrivate::TagInfo<T>::TagType(tagMask())); |
103 | } |
104 | |
105 | void setTag(Tag tag) |
106 | { |
107 | Q_ASSERT_X( |
108 | (static_cast<quintptr>(tag) & pointerMask()) == 0, |
109 | "QTaggedPointer<T, Tag>::setTag" , |
110 | "Tag is larger than allowed by number of available tag bits" ); |
111 | |
112 | d = (d & pointerMask()) | static_cast<quintptr>(tag); |
113 | } |
114 | |
115 | Tag tag() const noexcept |
116 | { |
117 | return TagType(typename QtPrivate::TagInfo<T>::TagType(d & tagMask())); |
118 | } |
119 | |
120 | T* data() const noexcept |
121 | { |
122 | return reinterpret_cast<T*>(d & pointerMask()); |
123 | } |
124 | |
125 | bool isNull() const noexcept |
126 | { |
127 | return !data(); |
128 | } |
129 | |
130 | void swap(QTaggedPointer &other) noexcept |
131 | { |
132 | std::swap(d, other.d); |
133 | } |
134 | |
135 | friend inline bool operator==(QTaggedPointer lhs, QTaggedPointer rhs) noexcept |
136 | { |
137 | return lhs.data() == rhs.data(); |
138 | } |
139 | |
140 | friend inline bool operator!=(QTaggedPointer lhs, QTaggedPointer rhs) noexcept |
141 | { |
142 | return lhs.data() != rhs.data(); |
143 | } |
144 | |
145 | friend inline bool operator==(QTaggedPointer lhs, std::nullptr_t) noexcept |
146 | { |
147 | return lhs.isNull(); |
148 | } |
149 | |
150 | friend inline bool operator==(std::nullptr_t, QTaggedPointer rhs) noexcept |
151 | { |
152 | return rhs.isNull(); |
153 | } |
154 | |
155 | friend inline bool operator!=(QTaggedPointer lhs, std::nullptr_t) noexcept |
156 | { |
157 | return !lhs.isNull(); |
158 | } |
159 | |
160 | friend inline bool operator!=(std::nullptr_t, QTaggedPointer rhs) noexcept |
161 | { |
162 | return !rhs.isNull(); |
163 | } |
164 | |
165 | friend inline bool operator!(QTaggedPointer ptr) noexcept |
166 | { |
167 | return !ptr.data(); |
168 | } |
169 | |
170 | friend inline void swap(QTaggedPointer &p1, QTaggedPointer &p2) noexcept |
171 | { |
172 | p1.swap(p2); |
173 | } |
174 | |
175 | protected: |
176 | quintptr d; |
177 | }; |
178 | |
179 | template <typename T, typename Tag> |
180 | constexpr inline std::size_t qHash(QTaggedPointer<T, Tag> p, std::size_t seed = 0) noexcept |
181 | { return qHash(p.data(), seed); } |
182 | |
183 | template <typename T, typename Tag> |
184 | class QTypeInfo<QTaggedPointer<T, Tag>> |
185 | : public QTypeInfoMerger<QTaggedPointer<T, Tag>, quintptr> {}; |
186 | |
187 | QT_END_NAMESPACE |
188 | |
189 | #endif // QTAGGEDPOINTER_H |
190 | |