These functions project a point in the plane onto the surface of a
Riemann Sphere, the one-point compactification of the complex plane.
Each finite point
Every complex infinite value is projected to a single infinite value,
namely to positive infinity on the real axis.
These functions first appeared in glibc in version 2.1.
For an explanation of the terms used in this section, see
C99, POSIX.1-2001, POSIX.1-2008.
In glibc 2.11 and earlier, the implementation does something different
projection onto a Riemann Sphere).
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