When startProgress, endProgress, and progress were all 0 (as provoked by tst_QPropertyAnimation::startWithoutStartValue()), we'd calculate 0/0 and ubsan complained: qvariantanimation.cpp:284:60: runtime error: division by zero Fix by detecting progress - startProgress == 0 and setting localProgress = 0.0 in that case. This is a logical result, even though it might not be what IEEE754 rules would have yielded. A more comprehensive change that aims to reliably keep localProgress ∈ [0,1] and thus avoid the infinities when endProgress == startProgress, is outside the scope of this patch, which deals only with the UBSan error. Pick-to: 6.3 6.2 5.15 Change-Id: I5258b054a2060006795f49fb1cd7604aea3ed46b Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io> Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>