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qHash: backport the q(u)int128-to-quint64 reduction trick to 32-bit 

I didn't do it in a template because the 32-bit code requires a
compatibility hack for Qt 6 and it's using an XOR of the high and low
parts.

Fixes: QTBUG-116080
Change-Id: I5dd50a1a7ca5424d9e7afffd17ae0ba5b9ff52f6
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
bb10
Thiago Macieira 2024-01-26 16:08:35 -08:00
parent 1d7950c946
commit 0d15c000ad
2 changed files with 19 additions and 6 deletions
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23
src/corelib/tools/qhashfunctions.h
View File

@ -104,7 +104,22 @@ Q_DECL_CONST_FUNCTION constexpr inline size_t qHash(quint64 key, size_t seed = 0
return QHashPrivate::hash(size_t(key), seed);
}
Q_DECL_CONST_FUNCTION constexpr inline size_t qHash(qint64 key, size_t seed = 0) noexcept
{ return qHash(quint64(key), seed); }
{
if constexpr (sizeof(qint64) > sizeof(size_t)) {
// Avoid QTBUG-116080: we XOR the top half with its own sign bit:
// - if the qint64 is in range of qint32, then signmask ^ high == 0
// (for Qt 7 only)
// - if the qint64 is in range of quint32, then signmask == 0 and we
// do the same as the quint64 overload above
quint32 high = quint32(quint64(key) >> 32);
quint32 low = quint32(quint64(key));
quint32 signmask = qint32(high) >> 31; // all zeroes or all ones
signmask = QT_VERSION_MAJOR > 6 ? signmask : 0;
low ^= signmask ^ high;
return qHash(low, seed);
}
return qHash(quint64(key), seed);
}
#if QT_SUPPORTS_INT128
constexpr size_t qHash(quint128 key, size_t seed = 0) noexcept
{
@ -112,10 +127,8 @@ constexpr size_t qHash(quint128 key, size_t seed = 0) noexcept
}
constexpr size_t qHash(qint128 key, size_t seed = 0) noexcept
{
// Avoid QTBUG-116080: we XOR the top half with its own sign bit:
// - if the qint128 is in range of qint64, then signmask ^ high == 0
// - if the qint128 is in range of quint64, then signmask == 0 and we
// do the same as the quint128 overload above
// Avoid QTBUG-116080: same as above, but with double the sizes and without
// the need for compatibility
quint64 high = quint64(quint128(key) >> 64);
quint64 low = quint64(quint128(key));
quint64 signmask = qint64(high) >> 63; // all zeroes or all ones

2
tests/auto/corelib/tools/qhashfunctions/tst_qhashfunctions.cpp
View File

@ -195,7 +195,7 @@ void tst_QHashFunctions::signedIntegerConsistency()
if (v32 == value) {
// because of QTBUG-116080, this may not match, but we can't guarantee
// it mismatches 100% of the time either
if constexpr (sizeof(size_t) > sizeof(int))
if constexpr (sizeof(size_t) > sizeof(int) || QT_VERSION_MAJOR > 6)
QCOMPARE(hs64, hs32);
}