c/numeric/complex/clog

@1-3@ Computes the complex natural (base-e) logarithm of with branch cut along the negative real axis. @4@ Type-generic macro: If has type,  is called. if has type,  is called, if  has type ,  is called. If is real or integer, then the macro invokes the corresponding real function. If is imaginary, the corresponding complex number version is called.

Return value
If no errors occur, the complex natural logarithm of is returned, in the range of a strip in the interval $[−iπ, +iπ]$ along the imaginary axis and mathematically unbounded along the real axis.

Error handling and special values
Errors are reported consistent with math_errhandling

If the implementation supports IEEE floating-point arithmetic,
 * The function is continuous onto the branch cut taking into account the sign of imaginary part
 * If is, the result is  and fe_divbyzero is raised
 * If is, the result is  and fe_divbyzero is raised
 * If is  (for any finite x), the result is
 * If is  (for any finite x), the result is  and fe_invalid may be raised
 * If is  (for any finite positive y), the result is
 * If is  (for any finite positive y), the result is
 * If is, the result is
 * If is, the result is
 * If is, the result is
 * If is  (for any finite y), the result is  and fe_invalid may be raised
 * If is, the result is
 * If is, the result is
 * If is, the result is