atan

fnreal atan(real x) @safe pure nothrow @nogc

Calculates the arc tangent of x, returning a value ranging from -π/2 to π/2.

x atan(x) invalid?
±0.0 ±0.0 no
±∞ NaN yes
fndouble atan(double x) @safe pure nothrow @nogc

ditto

fnfloat atan(float x) @safe pure nothrow @nogc

ditto