...by dropping the use of qIsNull(), which, in Qt 4, distinguished
between -0.0f and +0.0f.
But mathematically, whether x, y, z are ±0 doesn't change the fact
that the result is the identity element (x, y, z should contain the
identity element for addition and w the one for multiplication), or
the null element (additive identity).
So using qIsNull() was wrong even in Qt 4. In Qt 5, qIsNull() returns
true for both ±0, so we can just as well compare to 0.0f instead,
which allows to mark these functions constexpr (qIsNull() can't be).
Do so.
Change-Id: I78b1fa7890036dd3cb4de7f90b75d439f9835e73
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
ec73b5d4b8