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Fix quadratic behavior when converting from QVariant

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The old code called insert for each item, leading to constant
reallocation of the data structure. Instead rely on the fact
that a QVariantMap (as well as the variant list) is sorted, so
we can convert to the QJson data structure in one go without
lots of reallocations.

Task-number: QTBUG-44737
Change-Id: Id2d38d278fb9afa5e062c7353b4d4215bdfb993c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Lars Knoll 2015-03-18 08:49:09 +01:00 committed by Simon Hausmann
parent 03f1a69e9c
commit 4889269ff0
2 changed files with 86 additions and 6 deletions
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41
src/corelib/json/qjsonarray.cpp
View File

@ -256,8 +256,45 @@ QJsonArray QJsonArray::fromStringList(const QStringList &list)
QJsonArray QJsonArray::fromVariantList(const QVariantList &list)
{
QJsonArray array;
for (QVariantList::const_iterator it = list.constBegin(); it != list.constEnd(); ++it)
array.append(QJsonValue::fromVariant(*it));
if (list.isEmpty())
return array;
array.detach2(1024);
QVector<QJsonPrivate::Value> values;
values.resize(list.size());
QJsonPrivate::Value *valueData = values.data();
uint currentOffset = sizeof(QJsonPrivate::Base);
for (int i = 0; i < list.size(); ++i) {
QJsonValue val = QJsonValue::fromVariant(list.at(i));
bool latinOrIntValue;
int valueSize = QJsonPrivate::Value::requiredStorage(val, &latinOrIntValue);
if (!array.detach2(valueSize))
return QJsonArray();
QJsonPrivate::Value *v = valueData + i;
v->type = (val.t == QJsonValue::Undefined ? QJsonValue::Null : val.t);
v->latinOrIntValue = latinOrIntValue;
v->latinKey = false;
v->value = QJsonPrivate::Value::valueToStore(val, currentOffset);
if (valueSize)
QJsonPrivate::Value::copyData(val, (char *)array.a + currentOffset, latinOrIntValue);
currentOffset += valueSize;
array.a->size = currentOffset;
}
// write table
array.a->tableOffset = currentOffset;
if (!array.detach2(sizeof(QJsonPrivate::offset)*values.size()))
return QJsonArray();
memcpy(array.a->table(), values.constData(), values.size()*sizeof(uint));
array.a->length = values.size();
array.a->size = currentOffset + sizeof(QJsonPrivate::offset)*values.size();
return array;
}

51
src/corelib/json/qjsonobject.cpp
View File

@ -197,11 +197,54 @@ QJsonObject &QJsonObject::operator =(const QJsonObject &other)
*/
QJsonObject QJsonObject::fromVariantMap(const QVariantMap &map)
{
// ### this is implemented the trivial way, not the most efficient way
QJsonObject object;
for (QVariantMap::const_iterator it = map.constBegin(); it != map.constEnd(); ++it)
object.insert(it.key(), QJsonValue::fromVariant(it.value()));
if (map.isEmpty())
return object;
object.detach2(1024);
QVector<QJsonPrivate::offset> offsets;
QJsonPrivate::offset currentOffset;
currentOffset = sizeof(QJsonPrivate::Base);
// the map is already sorted, so we can simply append one entry after the other and
// write the offset table at the end
for (QVariantMap::const_iterator it = map.constBegin(); it != map.constEnd(); ++it) {
QString key = it.key();
QJsonValue val = QJsonValue::fromVariant(it.value());
bool latinOrIntValue;
int valueSize = QJsonPrivate::Value::requiredStorage(val, &latinOrIntValue);
bool latinKey = QJsonPrivate::useCompressed(key);
int valueOffset = sizeof(QJsonPrivate::Entry) + QJsonPrivate::qStringSize(key, latinKey);
int requiredSize = valueOffset + valueSize;
if (!object.detach2(requiredSize + sizeof(QJsonPrivate::offset))) // offset for the new index entry
return QJsonObject();
QJsonPrivate::Entry *e = reinterpret_cast<QJsonPrivate::Entry *>(reinterpret_cast<char *>(object.o) + currentOffset);
e->value.type = val.t;
e->value.latinKey = latinKey;
e->value.latinOrIntValue = latinOrIntValue;
e->value.value = QJsonPrivate::Value::valueToStore(val, (char *)e - (char *)object.o + valueOffset);
QJsonPrivate::copyString((char *)(e + 1), key, latinKey);
if (valueSize)
QJsonPrivate::Value::copyData(val, (char *)e + valueOffset, latinOrIntValue);
offsets << currentOffset;
currentOffset += requiredSize;
object.o->size = currentOffset;
}
// write table
object.o->tableOffset = currentOffset;
if (!object.detach2(sizeof(QJsonPrivate::offset)*offsets.size()))
return QJsonObject();
memcpy(object.o->table(), offsets.constData(), offsets.size()*sizeof(uint));
object.o->length = offsets.size();
object.o->size = currentOffset + sizeof(QJsonPrivate::offset)*offsets.size();
return object;
}