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