diff options
author | Lars Knoll <lars.knoll@nokia.com> | 2012-09-07 10:02:04 +0200 |
---|---|---|
committer | Qt by Nokia <qt-info@nokia.com> | 2012-09-07 18:41:22 +0200 |
commit | 3a48320fd6335d21451f07cb68336404177e2d87 (patch) | |
tree | 598a446840aad5740703c5019a44062c22a0c00a /src/corelib/tools/qvector.h | |
parent | 5b1bc864a91c3bdb02e36e7546dadebabb42fdec (diff) |
Fix performance regression when appending one vector to another
When appending a QVector to an existing vector the code would
unconditionally realloc the vector instead of first checking
whether we can do without. This gives a quadratic behaviour when
repeatedly appending a vector to another.
Change-Id: I2cd81253e6a8aec0bc4402e6fbda262435080966
Reviewed-by: Qt Doc Bot <qt_docbot@qt-project.org>
Reviewed-by: Simon Hausmann <simon.hausmann@nokia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Diffstat (limited to 'src/corelib/tools/qvector.h')
-rw-r--r-- | src/corelib/tools/qvector.h | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/src/corelib/tools/qvector.h b/src/corelib/tools/qvector.h index f3ef9b97c3..e52fb9a1be 100644 --- a/src/corelib/tools/qvector.h +++ b/src/corelib/tools/qvector.h @@ -650,8 +650,12 @@ QVector<T> &QVector<T>::fill(const T &from, int asize) template <typename T> QVector<T> &QVector<T>::operator+=(const QVector &l) { - int newSize = d->size + l.d->size; - reallocData(d->size, newSize); + uint newSize = d->size + l.d->size; + const bool isTooSmall = newSize > d->alloc; + if (!isDetached() || isTooSmall) { + QArrayData::AllocationOptions opt(isTooSmall ? QArrayData::Grow : QArrayData::Default); + reallocData(d->size, isTooSmall ? newSize : d->alloc, opt); + } if (d->alloc) { T *w = d->begin() + newSize; |