The cproj functions compute and return a projection of z onto
    the Riemann sphere: z projects to z, except that all complex
    infinities (even those with one infinite part and one NaN part)
    project to positive infinity on the real axis. If z has an
    infinite part, then cproj(z) is equivalent to:

    INFINITY + I * copysign(0.0, cimag(z))