heads up - Qt qreal difference on ARM

[Rex Dieter]

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