include/QtCore/qarraydata.h

0001 // Copyright (C) 2020 The Qt Company Ltd.
0002 // Copyright (C) 2019 Intel Corporation.
0003 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
0004 // Qt-Security score:significant reason:default
0005
0006 #ifndef QARRAYDATA_H
0007 #define QARRAYDATA_H
0008
0009 #include <QtCore/qpair.h>
0010 #include <QtCore/qatomic.h>
0011 #include <QtCore/qflags.h>
0012 #include <QtCore/qcontainerfwd.h>
0013 #include <string.h>
0014
0015 QT_BEGIN_NAMESPACE
0016
0017 #if __has_cpp_attribute(gnu::malloc)
0018 #  define Q_DECL_MALLOCLIKE [[nodiscard, gnu::malloc]]
0019 #elif Q_CC_MSVC_ONLY
0020 #  define Q_DECL_MALLOCLIKE [[nodiscard]] __declspec(allocator) __declspec(restrict)
0021 #else
0022 #  define Q_DECL_MALLOCLIKE [[nodiscard]]
0023 #endif
0024
0025 template <class T> struct QTypedArrayData;
0026
0027 template <class T>
0028 struct QTypedArrayAllocationResult
0029 {
0030     QTypedArrayData<T> *header;
0031     T *ptr;
0032
0033     [[deprecated]]
0034     operator std::pair<QTypedArrayData<T>*, T*>() const noexcept { return {header, ptr}; }
0035 };
0036
0037 struct QArrayData
0038 {
0039     enum AllocationOption {
0040         Grow,
0041         KeepSize
0042     };
0043
0044     enum GrowthPosition {
0045         GrowsAtEnd,
0046         GrowsAtBeginning
0047     };
0048
0049    enum ArrayOption {
0050         ArrayOptionDefault = 0,
0051         CapacityReserved     = 0x1  //!< the capacity was reserved by the user, try to keep it
0052     };
0053     Q_DECLARE_FLAGS(ArrayOptions, ArrayOption)
0054
0055     QBasicAtomicInt ref_;
0056     ArrayOptions flags;
0057     qsizetype alloc;
0058
0059     qsizetype allocatedCapacity() noexcept
0060     {
0061         return alloc;
0062     }
0063
0064     qsizetype constAllocatedCapacity() const noexcept
0065     {
0066         return alloc;
0067     }
0068
0069     /// Returns true if sharing took place
0070     bool ref() noexcept
0071     {
0072         ref_.refRelaxed(); // suffices for ref-counting
0073         return true;
0074     }
0075
0076     /// Returns false if deallocation is necessary
0077     bool deref() noexcept
0078     {
0079         return ref_.deref();
0080     }
0081
0082     bool isShared() const noexcept
0083     {
0084         return ref_.loadRelaxed() != 1;
0085     }
0086
0087     // Returns true if a detach is necessary before modifying the data
0088     // This method is intentionally not const: if you want to know whether
0089     // detaching is necessary, you should be in a non-const function already
0090     bool needsDetach() noexcept
0091     {
0092         return ref_.loadRelaxed() > 1;
0093     }
0094
0095     qsizetype detachCapacity(qsizetype newSize) const noexcept
0096     {
0097         if (flags & CapacityReserved && newSize < constAllocatedCapacity())
0098             return constAllocatedCapacity();
0099         return newSize;
0100     }
0101
0102     Q_DECL_MALLOCLIKE
0103     static Q_CORE_EXPORT void *allocate(QArrayData **pdata, qsizetype objectSize, qsizetype alignment,
0104             qsizetype capacity, AllocationOption option = QArrayData::KeepSize) noexcept;
0105     Q_DECL_MALLOCLIKE
0106     static Q_CORE_EXPORT void *allocate1(QArrayData **pdata, qsizetype capacity,
0107                                          AllocationOption option = QArrayData::KeepSize) noexcept;
0108     Q_DECL_MALLOCLIKE
0109     static Q_CORE_EXPORT void *allocate2(QArrayData **pdata, qsizetype capacity,
0110                                          AllocationOption option = QArrayData::KeepSize) noexcept;
0111
0112     [[nodiscard]] static Q_CORE_EXPORT std::pair<QArrayData *, void *> reallocateUnaligned(QArrayData *data, void *dataPointer,
0113             qsizetype objectSize, qsizetype newCapacity, AllocationOption option) noexcept;
0114     static Q_CORE_EXPORT void deallocate(QArrayData *data, qsizetype objectSize,
0115             qsizetype alignment) noexcept;
0116 };
0117
0118 Q_DECLARE_OPERATORS_FOR_FLAGS(QArrayData::ArrayOptions)
0119
0120 namespace QtPrivate {
0121 // QArrayData with strictest alignment requirements supported by malloc()
0122 #if defined(Q_PROCESSOR_X86_32) && defined(Q_CC_GNU)
0123 // GCC's definition is incorrect since GCC 8 (commit r240248 in SVN; commit
0124 // 63012d9a57edc950c5f30242d1e19318b5708060 in Git). This is applied to all
0125 // GCC-like compilers in case they decide to follow GCC's lead in being wrong.
0126 constexpr size_t MaxPrimitiveAlignment = 2 * sizeof(void *);
0127 #else
0128 constexpr size_t MaxPrimitiveAlignment = alignof(std::max_align_t);
0129 #endif
0130
0131 struct alignas(MaxPrimitiveAlignment) AlignedQArrayData : QArrayData
0132 {
0133 };
0134 }
0135
0136 template <class T>
0137 struct QTypedArrayData
0138     : QArrayData
0139 {
0140     struct AlignmentDummy { QtPrivate::AlignedQArrayData header; T data; };
0141
0142     [[nodiscard]] static QTypedArrayAllocationResult<T>
0143     allocate(qsizetype capacity, AllocationOption option = QArrayData::KeepSize)
0144     {
0145         static_assert(sizeof(QTypedArrayData) == sizeof(QArrayData));
0146         QArrayData *d;
0147         void *result;
0148         if constexpr (sizeof(T) == 1) {
0149             // necessarily, alignof(T) == 1
0150             result = allocate1(&d, capacity, option);
0151         } else if constexpr (sizeof(T) == 2) {
0152             // alignof(T) may be 1, but that makes no difference
0153             result = allocate2(&d, capacity, option);
0154         } else {
0155             result = QArrayData::allocate(&d, sizeof(T), alignof(AlignmentDummy), capacity, option);
0156         }
0157 #if __has_builtin(__builtin_assume_aligned)
0158         // and yet we do offer results that have stricter alignment
0159         result = __builtin_assume_aligned(result, Q_ALIGNOF(AlignmentDummy));
0160 #endif
0161         return {static_cast<QTypedArrayData *>(d), static_cast<T *>(result)};
0162     }
0163
0164     static QTypedArrayAllocationResult<T>
0165     reallocateUnaligned(QTypedArrayData *data, T *dataPointer, qsizetype capacity, AllocationOption option)
0166     {
0167         static_assert(sizeof(QTypedArrayData) == sizeof(QArrayData));
0168         std::pair<QArrayData *, void *> pair =
0169                 QArrayData::reallocateUnaligned(data, dataPointer, sizeof(T), capacity, option);
0170         return {static_cast<QTypedArrayData *>(pair.first), static_cast<T *>(pair.second)};
0171     }
0172
0173     static void deallocate(QArrayData *data) noexcept
0174     {
0175         static_assert(sizeof(QTypedArrayData) == sizeof(QArrayData));
0176         QArrayData::deallocate(data, sizeof(T), alignof(AlignmentDummy));
0177     }
0178
0179     static T *dataStart(QArrayData *data, qsizetype alignment) noexcept
0180     {
0181         // Alignment is a power of two
0182         Q_ASSERT(alignment >= qsizetype(alignof(QArrayData)) && !(alignment & (alignment - 1)));
0183         void *start =  reinterpret_cast<void *>(
0184             (quintptr(data) + sizeof(QArrayData) + alignment - 1) & ~(alignment - 1));
0185         return static_cast<T *>(start);
0186     }
0187
0188     constexpr static qsizetype maxSize() noexcept
0189     {
0190         // -1 to deal with the pointer one-past-the-end
0191         return (QtPrivate::MaxAllocSize - sizeof(QtPrivate::AlignedQArrayData) - 1) / sizeof(T);
0192     }
0193     constexpr static qsizetype max_size() noexcept
0194     {
0195         return maxSize();
0196     }
0197 };
0198
0199 namespace QtPrivate {
0200 struct Q_CORE_EXPORT QContainerImplHelper
0201 {
0202     enum CutResult { Null, Empty, Full, Subset };
0203     static constexpr CutResult mid(qsizetype originalLength, qsizetype *_position, qsizetype *_length)
0204     {
0205         qsizetype &position = *_position;
0206         qsizetype &length = *_length;
0207         if (position > originalLength) {
0208             position = 0;
0209             length = 0;
0210             return Null;
0211         }
0212
0213         if (position < 0) {
0214             if (length < 0 || length + position >= originalLength) {
0215                 position = 0;
0216                 length = originalLength;
0217                 return Full;
0218             }
0219             if (length + position <= 0) {
0220                 position = length = 0;
0221                 return Null;
0222             }
0223             length += position;
0224             position = 0;
0225         } else if (size_t(length) > size_t(originalLength - position)) {
0226             length = originalLength - position;
0227         }
0228
0229         if (position == 0 && length == originalLength)
0230             return Full;
0231
0232         return length > 0 ? Subset : Empty;
0233     }
0234 };
0235 }
0236
0237 #undef Q_DECL_MALLOCLIKE
0238
0239 QT_END_NAMESPACE
0240
0241 #endif // include guard