Details
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Bug
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Resolution: Fixed
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P2: Important
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6.2.3, 6.5.1
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None
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Linux/Other display system
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8739963c8 (dev), f003d43eb (6.6)
Description
A compile error in qbitarray.h, could be a compiler bug, or an actual error that isn't detected when the code is unfolded. To reproduce, pass something unsigned to QBitArray::testBit() - could be simpler ways to reproduce also. In our code we declared an enum of type unsigned, and passed one of the values to QBitArray::testBit().
qt/include/QtCore/qbitarray.h:86:10: error: array subscript 1 is outside array bounds of 'const char [1]' [-Werror=array-bounds=] 86 | return (*(reinterpret_cast<const uchar*>(d.constData())+1+(i>>3)) & (1 << (i & 7))) != 0; }
Code in question:
inline bool QBitArray::testBit(qsizetype i) const
{ Q_ASSERT(size_t(i) < size_t(size()));
return (*(reinterpret_cast<const uchar*>(d.constData())+1+(i>>3)) & (1 << (i & 7))) != 0; }
Unfolding the code removes the compile error, note that this generates the exact same assembly when built:
inline bool QBitArray::testBit(qsizetype i) const
{
Q_ASSERT(size_t(i) < size_t(size()));
const auto *castedDataPointer = reinterpret_cast<const uchar*>(d.constData());
castedDataPointer += 1 + (i >> 3);
const auto dataByte = *castedDataPointer;
const auto bitLocation = 1 << (i & 7);
return (dataByte & bitLocation) != 0;
}