[Qt5-feedback] Real 64 Bit support ?

[Yves Bailly]

Le 12/05/2011 14:42, André Pönitz a écrit :
> On Thursday 12 May 2011 13:58:48 ext Keith Gardner wrote:
>> I would also like to see this. On top of a 64-bit build, I would like to see
>> the container classes (QVector, QList, etc...) have a qint64 to index the
>> values instead of a qint32.
>
> qint64 is expensive on (at least some) 32 bit machines.

True.

> Having _different_ sizes (32/64 bit) depending on architecture spoils
> cross-platform data exchange using e.g. QDataStream. So that's even
> less of an option.

Data exchange implies serializing things in a very controlled way, isn't it?
I avoid sending a mere "int" through a QDataStream, I always cast it to a
known-size type, e.g. int32_t or int64_t (depending on the needs). I would
treat "size_t" just the same way, so no data exchange problem.

> Having 31 bit for sizes is definitely "good enough" for all kinds of
> "mainstream" use cases.

True (mostly).

>>> For what it worths, I totally second this: true 64bits support is a real
>>> need, having to manage really huge datasets - here "huge" can mean
>>> far more than 4GB.
>
> On a quick glance, I think the limit can be raised to only affect the item
> count, not the size by changing two lines in QVectorData::malloc and grow.
>
> For 'double' data the size limit would be 16 GB then, and I am pretty sure
> you would have switched to non-shared container long before that.

Actually it wasn't about the index type, just about the memory available to
the running program. Imagine a big hash table, a deep bounding volumes hierarchy,
to operate on millions of triangles: for sure 32bits is enough to index each
object, but the whole complex, cross-inter-related structure can eat lots of
GB of RAM - more than a 32bits program can handle.

Regards,

-- 
      /- Yves Bailly - Software developper  -\
      \- Sescoi R&D  - http://www.sescoi.fr -/
"The possible is done. The impossible is being done. For miracles,
thanks to allow a little delay."