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author | Marc Mutz <marc.mutz@kdab.com> | 2021-08-12 08:56:46 +0200 |
---|---|---|
committer | Marc Mutz <marc.mutz@kdab.com> | 2021-08-27 12:42:57 +0200 |
commit | 4cbcdf62bdaf7679457fe6609f70a36c29497530 (patch) | |
tree | b97247e9055c72f2e6f44cf3a481e866a10927b6 | |
parent | 68c03d7ea44250387f5dfed2cf03dea08b7ddb7f (diff) | |
download | qtbase-4cbcdf62bdaf7679457fe6609f70a36c29497530.tar.gz |
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 05e0dfa0060aab80afc696161226b2ab0cddfbf9.
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)
Change-Id: Ie456b71b39c118001987716e30642f08f5e8dcdb
Reviewed-by: MÃ¥rten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit bd52059eef7c96031972b5bee03067f3cb0f038d)
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
-rw-r--r-- | src/corelib/kernel/qmetaobject.cpp | 35 |
1 files changed, 32 insertions, 3 deletions
diff --git a/src/corelib/kernel/qmetaobject.cpp b/src/corelib/kernel/qmetaobject.cpp index 76a01f938e..40da8a3e4e 100644 --- a/src/corelib/kernel/qmetaobject.cpp +++ b/src/corelib/kernel/qmetaobject.cpp @@ -166,6 +166,13 @@ static inline const QByteArray stringData(const QMetaObject *mo, int index) return data; } +static inline QLatin1String stringDataView(const QMetaObject *mo, int index) +{ + const QByteArrayData &d = mo->d.stringdata[index]; + const char *string = reinterpret_cast<const char *>(d.data()); + return QLatin1String(string, d.size); +} + static inline const char *rawStringData(const QMetaObject *mo, int index) { return stringData(mo, index).data(); @@ -2819,6 +2826,28 @@ int QMetaEnum::keysToValue(const char *keys, bool *ok) const return value; } +namespace +{ +template <typename String, typename Container, typename Separator> +void join_reversed(String &s, const Container &c, Separator sep) +{ + if (c.empty()) + return; + qsizetype len = qsizetype(c.size()) - 1; // N - 1 separators + for (auto &e : c) + len += qsizetype(e.size()); // N parts + s.reserve(len); + bool first = true; + for (auto rit = c.rbegin(), rend = c.rend(); rit != rend; ++rit) { + const auto &e = *rit; + if (!first) + s.append(sep); + first = false; + s.append(e.data(), e.size()); + } +} +} // unnamed namespace + /*! Returns a byte array of '|'-separated keys that represents the given \a value. @@ -2833,17 +2862,17 @@ QByteArray QMetaEnum::valueToKeys(int value) const const int offset = priv(mobj->d.data)->revision >= 8 ? 3 : 2; int count = mobj->d.data[handle + offset]; int data = mobj->d.data[handle + offset + 1]; + QVarLengthArray<QLatin1String, sizeof(int) * CHAR_BIT> parts; int v = value; // reverse iterate to ensure values like Qt::Dialog=0x2|Qt::Window are processed first. for (int i = count - 1; i >= 0; --i) { int k = mobj->d.data[data + 2*i + 1]; if ((k != 0 && (v & k) == k ) || (k == value)) { v = v & ~k; - if (!keys.isEmpty()) - keys.prepend('|'); - keys.prepend(stringData(mobj, mobj->d.data[data + 2*i])); + parts.push_back(stringDataView(mobj, mobj->d.data[data + 2 * i])); } } + join_reversed(keys, parts, '|'); return keys; } |