c/numeric/complex/cpow

@1-3@ Computes the complex power function x$y$, with branch cut for the first parameter along the negative real axis. @4@ Type-generic macro: If any argument has type, is called. if any argument has type, is called, if any argument has type ,  is called. If the arguments are real or integer, then the macro invokes the corresponding real function. If any argument is imaginary, the corresponding complex number version is called.

Return value
If no errors occur, the complex power $xy$, is returned.

Errors and special cases are handled as if the operation is implemented by, except that the implementation is allowed to treat special cases more carefully.