[ajax77]

My reply wasn't meant as a numerically superior solution, simply as a fairly simple alternative without error codes...

As for "original specification", I'm not sure why you even bring that up. complex is certainly in the C++11 specification, against which my snippet is compliant.

[dalke]

Oh, I see I didn't explain well enough. I'm curious about how one would write the "numerically superior solution." That is, does C++11 have a templated copysign function which takes different numeric types (at least float, double, and quad)? If not, then there's some unneeded type promotion (or downcast) going on.

And if the template uses a float, how do I get the type with double precision to use as my intermediate? (And the same where the template uses a double and I want the intermediate to use a quad.)

There must surely be a way to handle these, but I haven't done C++ programming for over a decade and I don't know the modern way of doing things.

As regards "original specification" - I mean the original article from feabhas.com, which has since disappeared. As I recall, it only supported real roots, and not imaginary ones.

BTW, _Complex is also in C99.