cpp/numeric/math/tanh

@1-3@ Computes the hyperbolic tangent of.

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

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, ±0 is returned
 * If the argument is ±∞, ±1 is returned
 * if the argument is NaN, NaN is returned