The code is From Dr.Dobb's Journal: "Complex Arithmetic: In the Intersection of C and C++" By Randy Meyers and Dr. Thomas Plum, March 01, 2003
http://www.drdobbs.com/complex-arithmetic-in-the-intersection-o/184401628
The listing does not carry a license, however the educational spirit of the writing seems to suggest that it is intended for use by readers:
This month's installment does something a little different.
Rather than just discuss a new feature in C99 and occasionally
compare it to C++, we are going to concentrate on the
intersection between C99 and C++. We are going to discuss how
to write programs that use complex arithmetic and compile
equally well under either C++ or C99. The key to opening the
large intersection between C and C++ complex is the small
header file named math-complex.h (shown in Listing 1).
The file "math-complex.h" is the contents of the "Listing 1" link. The file "test-program.cpp.c99" is the contents of the "Listing 2" link. The file "test-program-results.txt" is the contents of the "Listing 3" link.