"Generally, mixed-mode arithmetic combining real and complex variables should be performed directly, not by first coercing the real to complex, lest the sign of zero be rendered uninformative; the same goes for combinations of pure imaginary quantities with complex variables." (c) Kahan, W: Branch cuts for complex elementary functions. This patch implements mixed-mode arithmetic rules, combining real and complex variables as specified by C standards since C99 (in particular, there is no special version for the true division with real lhs operand). Most C compilers implementing C99+ Annex G have only these special rules (without support for imaginary type, which is going to be deprecated in C2y).