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QHeaderView - create a union to save some space.

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Beside saving some space it also ensures a bit faster vector operations
(remove and insert memcpy) - and lower the risk for a cache-miss.
(Many operations seems to be about 5-10% faster in the benchmark).

Change-Id: If8109e2146c25f642015906375dfbb449706ce8e
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>
This commit is contained in:
Thorbjørn Lund Martsum 2012-02-20 16:11:31 +01:00 committed by Qt by Nokia
parent a4e4c31007
commit 13f3346d34
1 changed files with 5 additions and 3 deletions
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8
src/widgets/itemviews/qheaderview_p.h
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@ -287,8 +287,11 @@ public:
struct SectionSpan {
int size;
mutable int calculated_startpos;
mutable int tmpLogIdx;
union { // This union is made in order to save space and ensure good vector performance (on remove)
mutable int calculated_startpos; // <- this is the primary used member.
mutable int tmpLogIdx; // When one of these 'tmp'-members has been used we call
int tmpDataStreamSectionCount; // recalcSectionStartPos() or set sectionStartposRecalc to true
}; // to ensure that calculated_startpos will be calculated afterwards.
QHeaderView::ResizeMode resizeMode;
inline SectionSpan() : size(0), resizeMode(QHeaderView::Interactive) {}
inline SectionSpan(int length, QHeaderView::ResizeMode mode)
@ -296,7 +299,6 @@ public:
inline int sectionSize() const { return size; }
inline int calculatedEndPos() const { return calculated_startpos + size; }
#ifndef QT_NO_DATASTREAM
int tmpDataStreamSectionCount;
inline void write(QDataStream &out) const
{ out << size; out << 1; out << (int)resizeMode; }
inline void read(QDataStream &in)