AuroraMiddleware/qt5base-lts
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QMdiArea: fix quadratic behavior

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Repeatedly calling QVector::erase(it) (via QMutableVectorIterator::remove())
results in quadratic runtime.

Use std::stable_partition, which does exactly what the old code tried to do,
except in linear time.

Change-Id: I6e5911ee781071bbb84d72449c969e3b9907da51
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
This commit is contained in:
Marc Mutz 2015-12-03 13:47:27 +01:00
parent 0d1024e0f1
commit dc41ff5a84
1 changed files with 9 additions and 11 deletions
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20
src/widgets/widgets/qmdiarea.cpp
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@ -161,7 +161,6 @@
#include <QResizeEvent>
#include <QScrollBar>
#include <QtAlgorithms>
#include <QMutableVectorIterator>
#include <QPainter>
#include <QFontMetrics>
#include <QStyleOption>
@ -480,17 +479,16 @@ QVector<QRect> MinOverlapPlacer::getCandidatePlacements(const QSize &size, const
*/
QVector<QRect> MinOverlapPlacer::findNonInsiders(const QRect &domain, QVector<QRect> &source)
{
QVector<QRect> result;
result.reserve(source.size());
const auto containedInDomain =
[domain](const QRect &srcRect) { return domain.contains(srcRect); };
QMutableVectorIterator<QRect> it(source);
while (it.hasNext()) {
const QRect srcRect = it.next();
if (!domain.contains(srcRect)) {
result << srcRect;
it.remove();
}
}
const auto firstOut = std::stable_partition(source.begin(), source.end(), containedInDomain);
QVector<QRect> result;
result.reserve(source.end() - firstOut);
std::copy(firstOut, source.end(), std::back_inserter(result));
source.erase(firstOut, source.end());
return result;
}