On Thursday 07 November 2013 18:18:18 you wrote: > On Sat, Nov 02, 2013, Lisandro Damián Nicanor Pérez Meyer wrote: > > Hi! Starting from Qt 5.2.0 (most probably from rc1 and definitely not from > > beta1 currently in experimental) Qt5 will switch qreal from float to > > double on arm*. > > > > We have the option to keep some archs in float by passing a compilation > > parameter. I've done so for armel and sh4, so only armhf will switch to > > double. > > > > Of course we are still on time to discuss this, and this is the reason of > > this mail. What do you think WRT the above changes? > > First, thanks a lot for the heads up on this. Thank you too for replying :) > qreal being float instead of double on ARM was the source of a bunch of > work for ARM porters in the past; now I have these worries/questions: > * switching it back might imply some new porting work (in the case where > the patches were something #if ARM use float #else use double); this > might be particularly painful if armel and armhf have different > definitions. Maybe there's a nice define #QREAL_IS_FLOAT or something > to help with this. Don't forget we are talking about *just* Qt5 here, *not* Qt4. We only have 3 apps building against Qt5 right now. If apps switch to Qt5 they will surely find some bumps, so this can be managed. > * what about arm64? sounds like this one should be double from the > start; not sure what it is right now I have not added any provisions to arm64, so with the next 5.2.0 [rc/final] upload it will switch to double. We are still on time if something needs a fix here. > * when you say you've changed armel and sh4 to keep using float, is this > Debian-specific? Not sure we want a delta with upstream on this kind > of stuff. Would it not work at all to use double, or would it just be > slow? I'd rather have it slow for people using big software on slow > arches rather than keeping a delta; it sounds like we do a SONAME > transition no matter what anyway Now this *will* be messy. I have asked upstream  and so far haven't got any explicit reply from other distro's maintainers.  <http://lists.qt-project.org/pipermail/development/2013-November/014017.html> But, according to : "I should also point out that this option now allows selecting qreal to be float on other platforms, besides ARM." That's why I'm still spamming debian-ports ;)  <http://lists.qt-project.org/pipermail/development/2013-November/014017.html> So: - We don't know yet what other distros are going to do. - If we decide to do the change in Qt5, it will be *without* soname bump. Yes, I know many of you will think of this as **ugly**, but so far means 3 binNMUs per arch. Now if this is not acceptable, then no change will be made, because I won't change Qt5's SONAME. > * what's the point in qreal anyway? can't we just switch everything to > float or double? sounds like software should know what kind of level > of precision it needs in the first place; e.g. if it's a scale in some > UI, then either float or double is enough, but it's not an arch > specific decision I really don't know, it was already there when I started using Qt back in Qt3's final days ;-) But I *do* know that if people want it gone, they will need to wait until Qt6 and provide the necessary patches :-/ Hope that helps, Lisandro. -- Lisandro Damián Nicanor Pérez Meyer http://perezmeyer.com.ar/ http://perezmeyer.blogspot.com/
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