QMetaEnum: avoid quadratic behavior in valueToKeys()
QByteArray (thankfully) doesn't have the prepend "optimization", so
prepend() is a linear operation, calling it in a loop thus makes the
algorithm quadratic.
To fix, simply remember the parts in a QVLA (an upper bound on the
size of which is easily calculated) and then build the result by
reverse-iterating over the QVLA.
This join_reversed() function is possibly useful elsewhere, but I left
it locally in the unnamed namespace to ease cherry-picking.
The new stringDataView() function is more universally useful, too, and
will be used in a subsequent other change. It return QL1S instead of
QByteArrayView because the latter is scheduled to become a non-string
type, and already lacks certain features (e.g. qTokenize() doesn't
work on QBA, due to lack of a Qt::CaseSensitivity argument in
QBA::indexOf()). It's also a Qt 6 addition, so not available in
5.15. We can revisit this decision later, when QBAV (or, possibly,
QU8SV) has caught up.
Amends 05e0dfa006.
Results indicate a ~2x speedup:
PASS : tst_QMetaEnum::valueToKeys(1 bits set)
- 0.00026 msecs per iteration (total: 70, iterations: 262144)
+ 0.00017 msecs per iteration (total: 90, iterations: 524288)
PASS : tst_QMetaEnum::valueToKeys(2 bits set)
- 0.00037 msecs per iteration (total: 98, iterations: 262144)
+ 0.00019 msecs per iteration (total: 52, iterations: 262144)
PASS : tst_QMetaEnum::valueToKeys(3 bits set)
- 0.00040 msecs per iteration (total: 53, iterations: 131072)
+ 0.00021 msecs per iteration (total: 56, iterations: 262144)
PASS : tst_QMetaEnum::valueToKeys(4 bits set)
- 0.00047 msecs per iteration (total: 62, iterations: 131072)
+ 0.00022 msecs per iteration (total: 60, iterations: 262144)
PASS : tst_QMetaEnum::valueToKeys(5 bits set)
- 0.00048 msecs per iteration (total: 63, iterations: 131072)
+ 0.00024 msecs per iteration (total: 64, iterations: 262144)
PASS : tst_QMetaEnum::valueToKeys(6 bits set)
- 0.00061 msecs per iteration (total: 80, iterations: 131072)
+ 0.00027 msecs per iteration (total: 71, iterations: 262144)
PASS : tst_QMetaEnum::valueToKeys(7 bits set)
- 0.00063 msecs per iteration (total: 83, iterations: 131072)
+ 0.00027 msecs per iteration (total: 73, iterations: 262144)
PASS : tst_QMetaEnum::valueToKeys(8 bits set)
- 0.00069 msecs per iteration (total: 91, iterations: 131072)
+ 0.00030 msecs per iteration (total: 81, iterations: 262144)
PASS : tst_QMetaEnum::valueToKeys(9 bits set)
- 0.00070 msecs per iteration (total: 92, iterations: 131072)
+ 0.00031 msecs per iteration (total: 83, iterations: 262144)
PASS : tst_QMetaEnum::valueToKeys(10 bits set)
- 0.00074 msecs per iteration (total: 98, iterations: 131072)
+ 0.00034 msecs per iteration (total: 91, iterations: 262144)
PASS : tst_QMetaEnum::valueToKeys(11 bits set)
- 0.000762 msecs per iteration (total: 100, iterations: 131072)
+ 0.00035 msecs per iteration (total: 92, iterations: 262144)
PASS : tst_QMetaEnum::valueToKeys(12 bits set)
- 0.00088 msecs per iteration (total: 58, iterations: 65536)
+ 0.000381 msecs per iteration (total: 100, iterations: 262144)
PASS : tst_QMetaEnum::valueToKeys(13 bits set)
- 0.00094 msecs per iteration (total: 62, iterations: 65536)
+ 0.00038 msecs per iteration (total: 51, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(14 bits set)
- 0.00099 msecs per iteration (total: 65, iterations: 65536)
+ 0.00041 msecs per iteration (total: 55, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(15 bits set)
- 0.0010 msecs per iteration (total: 67, iterations: 65536)
+ 0.00042 msecs per iteration (total: 56, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(16 bits set)
- 0.0010 msecs per iteration (total: 70, iterations: 65536)
+ 0.00044 msecs per iteration (total: 58, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(17 bits set)
- 0.0011 msecs per iteration (total: 73, iterations: 65536)
+ 0.00046 msecs per iteration (total: 61, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(18 bits set)
- 0.0012 msecs per iteration (total: 79, iterations: 65536)
+ 0.00048 msecs per iteration (total: 63, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(19 bits set)
- 0.0012 msecs per iteration (total: 79, iterations: 65536)
+ 0.00051 msecs per iteration (total: 67, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(20 bits set)
- 0.0012 msecs per iteration (total: 80, iterations: 65536)
+ 0.00054 msecs per iteration (total: 71, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(21 bits set)
- 0.0012 msecs per iteration (total: 83, iterations: 65536)
+ 0.00090 msecs per iteration (total: 59, iterations: 65536)
PASS : tst_QMetaEnum::valueToKeys(22 bits set)
- 0.0012 msecs per iteration (total: 85, iterations: 65536)
+ 0.00057 msecs per iteration (total: 76, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(23 bits set)
- 0.0013 msecs per iteration (total: 87, iterations: 65536)
+ 0.00059 msecs per iteration (total: 78, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(24 bits set)
- 0.0014 msecs per iteration (total: 93, iterations: 65536)
+ 0.00065 msecs per iteration (total: 86, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(25 bits set)
- 0.0014 msecs per iteration (total: 94, iterations: 65536)
+ 0.00063 msecs per iteration (total: 83, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(26 bits set)
- 0.00028 msecs per iteration (total: 74, iterations: 262144)
+ 0.00017 msecs per iteration (total: 94, iterations: 524288)
PASS : tst_QMetaEnum::valueToKeys(27 bits set)
- 0.0014 msecs per iteration (total: 98, iterations: 65536)
+ 0.00063 msecs per iteration (total: 83, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(28 bits set)
- 0.0014 msecs per iteration (total: 96, iterations: 65536)
+ 0.00065 msecs per iteration (total: 86, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(29 bits set)
- 0.0014 msecs per iteration (total: 98, iterations: 65536)
+ 0.00064 msecs per iteration (total: 84, iterations: 131072)
PASS : tst_QMetaEnum::valueToKeys(30 bits set)
- 0.0014 msecs per iteration (total: 97, iterations: 65536)
+ 0.00064 msecs per iteration (total: 84, iterations: 131072)
Pick-to: 6.2 5.15
Change-Id: Ie456b71b39c118001987716e30642f08f5e8dcdb
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
bb10
Marc Mutz
parent
62572f0a18
commit
bd52059eef
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@ -157,13 +157,19 @@ static inline const char *rawStringData(const QMetaObject *mo, int index)
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return reinterpret_cast<const char *>(mo->d.stringdata) + offset;
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}
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static inline const QByteArray stringData(const QMetaObject *mo, int index)
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static inline QLatin1String stringDataView(const QMetaObject *mo, int index)
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{
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Q_ASSERT(priv(mo->d.data)->revision >= 7);
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uint offset = mo->d.stringdata[2*index];
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uint length = mo->d.stringdata[2*index + 1];
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const char *string = reinterpret_cast<const char *>(mo->d.stringdata) + offset;
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return QByteArray::fromRawData(string, length);
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return QLatin1String(string, length);
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}
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static inline QByteArray stringData(const QMetaObject *mo, int index)
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{
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const auto view = stringDataView(mo, index);
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return QByteArray::fromRawData(view.data(), view.size());
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}
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static inline const char *rawTypeNameFromTypeInfo(const QMetaObject *mo, uint typeInfo)
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@ -2874,6 +2880,28 @@ int QMetaEnum::keysToValue(const char *keys, bool *ok) const
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return value;
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}
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namespace
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{
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template <typename String, typename Container, typename Separator>
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void join_reversed(String &s, const Container &c, Separator sep)
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{
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if (c.empty())
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return;
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qsizetype len = qsizetype(c.size()) - 1; // N - 1 separators
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for (auto &e : c)
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len += qsizetype(e.size()); // N parts
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s.reserve(len);
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bool first = true;
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for (auto rit = c.rbegin(), rend = c.rend(); rit != rend; ++rit) {
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const auto &e = *rit;
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if (!first)
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s.append(sep);
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first = false;
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s.append(e.data(), e.size());
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}
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}
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} // unnamed namespace
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/*!
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Returns a byte array of '|'-separated keys that represents the
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given \a value.
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@ -2885,17 +2913,17 @@ QByteArray QMetaEnum::valueToKeys(int value) const
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QByteArray keys;
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if (!mobj)
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return keys;
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QVarLengthArray<QLatin1String, sizeof(int) * CHAR_BIT> parts;
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int v = value;
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// reverse iterate to ensure values like Qt::Dialog=0x2|Qt::Window are processed first.
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for (int i = data.keyCount() - 1; i >= 0; --i) {
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int k = mobj->d.data[data.data() + 2 * i + 1];
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if ((k != 0 && (v & k) == k) || (k == value)) {
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v = v & ~k;
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if (!keys.isEmpty())
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keys.prepend('|');
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keys.prepend(stringData(mobj, mobj->d.data[data.data() + 2 * i]));
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parts.push_back(stringDataView(mobj, mobj->d.data[data.data() + 2 * i]));
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}
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}
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join_reversed(keys, parts, '|');
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return keys;
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}
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