cproj(3) -- Linux man page
NAMEcproj, cprojf, cprojl - project into Riemann Sphere
double complex cproj(double complex z);
float complex cprojf(float complex z);
long double complex cprojl(long double complex z);
DESCRIPTIONWith this function you can project a point in the plane onto the surface of a Riemann Sphere, the one-point compactification of the complex plane. Each finite point z projects to z itself. Every complex infinite values is projected to a single infinite value, namely to positive infinity on the real axis.