heads up - Qt qreal difference on ARM
Rex Dieter
rdieter at fedoraproject.org
Fri Aug 2 12:27:12 UTC 2013
On 08/01/2013 11:49 PM, Orion Poplawski wrote:
> http://doc.qt.digia.com/4.6/qtglobal.html#qreal-typedef
>
> typedef qreal
>
> Typedef for double on all platforms except for those using CPUs with ARM
> architectures. On ARM-based platforms, qreal is a typedef for float for
> performance reasons.
>
> This still seems to be the case for 4.8 as well.
>
> This lead to the following compile error on arm in kst:
>
> /builddir/build/BUILD/kst-2.0.7/src/libkstapp/plotrenderitem.cpp:561:33:
> error: no matching function for call to 'qMin(double&, qreal)'
> y = qMin(y, plotItem()->yMax());
> ^
>
> If there is scientific type codes using qreal this might lead to some
> precision issues as well.
Yes, we've had to patch quite a few packages to fix/workaround
qreal!=double assumptions in code.
> Is double really that much slower on arm?
Good question for
https://lists.fedoraproject.org/mailman/listinfo/arm
(but, I assume the qt docs aren't lying and the answer is yes)
-- rex
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