>> I don't understand why Emacs doesn't support signed zero.
>> For example in JavaScript: Math.sign(-0) => -0
>
> It does, for floats (afaik, in JavaScript all numbers are floating
> point).
>
>     (copysign 1.0 -0.0) ;=> -1.0

Then if take into use floats, the distinction could be
not between positive/negative floats, but between integers/floats.

Joćo, could you please try a new patch: