[cfe-dev] [libc++] std::polar(rho, theta) bogus for theta < 0?

[Luc Bourhis]

Hi,

polar(rho, theta) returns (NaN, NaN) if rho < 0. The code responsible for that behaviour is in the first two lines of the body of polar:

    if (isnan(__rho) || signbit(__rho))
        return complex<_Tp>(_Tp(NAN), _Tp(NAN));

libstdc++, on the contrary, returns (rho*cos(theta), rho*sin(theta)) in this case.

The standard says "Returns: the complex value corresponding to a complex number whose magnitude is rho and whose phase angle is theta."
It seems to favour libc++ choice over libstdc++ one but it is a real pain when the two major standard libraries on current platforms disagree in such a manner.
We have hit that bug hard in the Computational Crystallography Toolbox, which has to run on MacOS, Linuxes (and Windows but that's another story).

Thanks,

Luc J. Bourhis