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QBitArray: refactor operator~() to write to an uninitialized buffer

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No functionality change otherwise.

Change-Id: I85b3fc2dd45c4693be13fffd179627b2747c132b
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
This commit is contained in:
Thiago Macieira 2023-11-09 20:12:36 -08:00
parent 9323351695
commit 9b176281df
2 changed files with 21 additions and 10 deletions
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28
src/corelib/tools/qbitarray.cpp
View File

@ -594,18 +594,26 @@ QBitArray &QBitArray::operator^=(const QBitArray &other)
QBitArray QBitArray::operator~() const
{
qsizetype sz = size();
QBitArray a(sz);
const uchar *a1 = reinterpret_cast<const uchar *>(d.constData()) + 1;
uchar *a2 = reinterpret_cast<uchar *>(a.d.data()) + 1;
qsizetype n = d.size() - 1;
qsizetype n = d.size();
QBitArray result(QByteArrayData(n, n));
const uchar *src = reinterpret_cast<const uchar *>(data_ptr().data());
uchar *dst = reinterpret_cast<uchar *>(result.data_ptr().data());
while (n-- > 0)
*a2++ = ~*a1++;
uchar bitdiff = 8;
if (n)
bitdiff = dst[0] = src[0]; // copy the count of bits in the last byte
if (sz && sz % 8)
*(a2 - 1) &= (1 << (sz % 8)) - 1;
return a;
for (qsizetype i = 1; i < n; ++i)
dst[i] = ~src[i];
if (int tailCount = 16 - bitdiff; tailCount != 8) {
// zero the bits beyond our size in the last byte
Q_ASSERT(n > 1);
uchar tailMask = (1U << tailCount) - 1;
dst[n - 1] &= tailMask;
}
return result;
}
/*!

3
src/corelib/tools/qbitarray.h
View File

@ -18,6 +18,8 @@ class Q_CORE_EXPORT QBitArray
friend Q_CORE_EXPORT size_t qHash(const QBitArray &key, size_t seed) noexcept;
QByteArray d;
QBitArray(QByteArrayData &&dd) : d(std::move(dd)) {}
template <typename BitArray> static auto bitLocation(BitArray &ba, qsizetype i)
{
Q_ASSERT(size_t(i) < size_t(ba.size()));
@ -95,6 +97,7 @@ public:
public:
typedef QByteArray::DataPointer DataPtr;
inline DataPtr &data_ptr() { return d.data_ptr(); }
inline const DataPtr &data_ptr() const { return d.data_ptr(); }
};