cpp/numeric/math/tan

@1-3@ Computes the tangent of (measured in radians).

Return value
If no errors occur, the tangent of ($tan(num)$) is returned.

If a domain error occurs, an implementation-defined value is returned (NaN where supported).

If a range error occurs due to underflow, the correct result (after rounding) is returned.

Error handling
Errors are reported as specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),
 * if the argument is ±0, it is returned unmodified
 * if the argument is ±∞, NaN is returned and fe_invalid is raised
 * if the argument is NaN, NaN is returned