Implementation of qFuzzyCompare and zero values

[j1elo]

Hello all,
I'm using qFuzzyCompare(a, b) in order to handle all floating point comparisons, but it has severe limitations when a or b may be zero.

Somewhere in the docs it is recommended to add +1 to the values, but this is not a really useful suggestion because some of the values might be -1.0, resulting in 0.0 after the addition.

So far, in each file which needs to perform floating point comparisons, I'm using the following macro:

@
#include <QtGlobal> // qMax, qMin, qFuzzyCompare
#define qFuzzyCompare(a, b) (qFuzzyIsNull(a) && qFuzzyIsNull(b)) || qFuzzyCompare((a), (b))
@

But instead of ad-hoc workarounds, IMHO this caveat should be fixed straight in the implementation of the qFuzzyCompare() function. A really old bug report already exists: "QTBUG-16819":https://bugreports.qt-project.org/browse/QTBUG-16819 it is open but it seems that discussion ended on 2011 for some reason.

Could anyone add a bit more on this subject?

[JKSH]

Hmm... I'm not familiar with this issue, but it does look like something that could be handled better by the library itself.

You can post to the "Development mailing list":http://lists.qt-project.org/mailman/listinfo/development to start a discussion with Qt's engineers.

[tonyorourke]

My guess is the good folks at Qt aren't interested because the good folks at Qt don't use qFuzzyCompare themselves; instead, they favour a set of 'qFsk...' routines which you'll find here -

C:\Qt3d\src\threed\geometry\qvector_utils_p.h

(or somewhere like it, depending on where your Qt3d source code is)

The routines you find there should solve your problems.