c/numeric/math/tgamma

@1-3@ Computes the of. @4@ Type-generic macro: If has type,  is called. Otherwise, if has integer type or the type,  is called. Otherwise, is called.

Return value
If no errors occur, the value of the gamma function of, that is , is returned.

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

If a pole error occurs, huge_val,, or is returned.

If a range error due to overflow occurs, huge_val,, or is returned.

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

Error handling
Errors are reported as specified in.

If is zero or is an integer less than zero, a pole error or a domain error may occur.

If the implementation supports IEEE floating-point arithmetic (IEC 60559):
 * If the argument is ±0, ±∞ is returned and fe_divbyzero is raised.
 * If the argument is a negative integer, NaN is returned and fe_invalid is raised.
 * If the argument is -∞, NaN is returned and fe_invalid is raised.
 * If the argument is +∞, +∞ is returned.
 * If the argument is NaN, NaN is returned.