A dangerous topic for everyone :-)
I've been working with some unittests involving comparing the output of
different but theoretically equivalent versions of the same calculation. To my
surprise, calculations which I assumed would produce identical output, were
failing equality tests.
It seemed unlikely this would be due to any kind of different rounding error,
but I decided to check by writing out the whole floating-point numbers formatted
with %.80f. This confirmed my suspicion that the numbers were indeed identical.
You can read the detailed story here:
https://github.com/D-Programming-Language/phobos/pull/1740
It seems like I can probably use isIdentical for the unittests, but I am more
concerned about the equality operator. I completely understand that equality
comparisons between FP are dangerous in general as tiny rounding errors may
induce a difference, but == in D seems to see difference in circumstances where
(so far as I can see) it really shouldn't happen.
Can anybody offer an explanation, a prognosis for improving things, and possible
coping strategies in the meantime (other than the ones I already know,
isIdentical and approxEqual)?
