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Optimize QSet set operations 

Replace the identity check with a check for the underlying QHash
objects being shared and replace backwards iteration, which is really
forwards iteration with wrapping at bucket boundaries, with forward
iteration. QSet cannot contain duplicates, so the order in which the
RHS elements are presented to the algorithms does not matter.

Change-Id: Iad8528e3a9501b14cb85601b221a848aad91480c
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
bb10
Marc Mutz 2019-07-02 10:16:43 +02:00
parent e40a139abf
commit e1c9276c77
1 changed files with 9 additions and 16 deletions
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25
src/corelib/tools/qset.h
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@ -284,11 +284,9 @@ Q_INLINE_TEMPLATE void QSet<T>::reserve(int asize) { q_hash.reserve(asize); }
template <class T>
Q_INLINE_TEMPLATE QSet<T> &QSet<T>::unite(const QSet<T> &other)
{
QSet<T> copy(other);
typename QSet<T>::const_iterator i = copy.constEnd();
while (i != copy.constBegin()) {
--i;
insert(*i);
if (!q_hash.isSharedWith(other.q_hash)) {
for (const T &e : other)
insert(e);
}
return *this;
}
@ -306,11 +304,9 @@ Q_INLINE_TEMPLATE QSet<T> &QSet<T>::intersect(const QSet<T> &other)
copy2 = *this;
*this = copy1;
}
typename QSet<T>::const_iterator i = copy1.constEnd();
while (i != copy1.constBegin()) {
--i;
if (!copy2.contains(*i))
remove(*i);
for (const auto &e : qAsConst(copy1)) {
if (!copy2.contains(e))
remove(e);
}
return *this;
}
@ -346,14 +342,11 @@ Q_INLINE_TEMPLATE bool QSet<T>::intersects(const QSet<T> &other) const
template <class T>
Q_INLINE_TEMPLATE QSet<T> &QSet<T>::subtract(const QSet<T> &other)
{
if (&other == this) {
if (q_hash.isSharedWith(other.q_hash)) {
clear();
} else {
auto i = other.constEnd();
while (i != other.constBegin()) {
--i;
remove(*i);
}
for (const auto &e : other)
remove(e);
}
return *this;
}