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tst_QHashSeed: improve quality of the quality() test

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We expect to produce all-bits-set in the combined OR'ed value of the
seed, so instead of counting how many bits got set and reporting that,
simply compare to -1 and count how long it took to get that far.

To make sure, I've increased the number of iterations by 50%.

Change-Id: I89446ea06b5742efb194fffd16ba37b2d93c19ef
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
This commit is contained in:
Thiago Macieira 2021-11-23 10:41:52 -08:00
parent e75b1dfe38
commit 84c9fcffee
1 changed files with 15 additions and 10 deletions
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25
tests/auto/corelib/tools/qhashseed/tst_qhashseed.cpp
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@ -137,9 +137,10 @@ void tst_QHashSeed::quality()
// this "bad seed" is used internally in qhash.cpp and should never leak!
constexpr size_t BadSeed = size_t(Q_UINT64_C(0x5555'5555'5555'5555));
constexpr int Iterations = 16;
constexpr int Iterations = 24; // nicely divisible by 3
int oneThird = 0;
int badSeeds = 0;
int seedsToMinus1 = 0;
size_t ored = 0;
for (int i = 0; i < Iterations; ++i) {
@ -152,29 +153,33 @@ void tst_QHashSeed::quality()
++oneThird;
if (seed == BadSeed)
++badSeeds;
if (ored != size_t(-1))
++seedsToMinus1;
QHashSeed::resetRandomGlobalSeed();
}
// report out
qInfo() << "Number of seeds until all bits became set:" << seedsToMinus1 << '/' << Iterations;
qInfo() << "Number of seeds with at least one third of the bits set:"
<< oneThird << '/' << Iterations;
qInfo() << "Number of bits in OR'ed value:" << qPopulationCount(quintptr(ored))
<< '/' << std::numeric_limits<size_t>::digits;
if (std::numeric_limits<size_t>::digits > 32) {
quint32 upper = quint64(ored) >> 32;
qInfo() << "Number of bits in the upper half:" << qPopulationCount(upper) << "/ 32";
QVERIFY(qPopulationCount(upper) > (32/3));
}
// we must have set all bits after all the iterations
QCOMPARE(ored, size_t(-1));
// at least one third of the seeds must have one third of all the bits set
QVERIFY(oneThird > (16/3));
QVERIFY(oneThird > (Iterations/3));
// at most one seed can be the bad seed, if 32-bit, none on 64-bit
if (std::numeric_limits<size_t>::digits > 32)
QCOMPARE(badSeeds, 0);
else
QVERIFY(badSeeds <= 1);
QVERIFY2(badSeeds <= 1, "badSeeds = " + QByteArray::number(badSeeds));
// we must have taken at most two thirds of the iterations to have set each
// bit at least once
QVERIFY2(seedsToMinus1 < 2*Iterations/3,
"seedsToMinus1 = " + QByteArray::number(seedsToMinus1));
}
#if QT_VERSION < QT_VERSION_CHECK(7, 0, 0)