Re: Fortran pow (complex ** huge) returns NaN instead of Inf ?

[Tobias Schlüter <tobias dot schlueter at physik dot uni-muenchen dot de>]

Hi Kaveh,

Kaveh R. Ghazi wrote:
> The testcase has on lines 41/42 these statements:
>
>  print *, (2.0,-4.3)**huge(0) ! { dg-error "Arithmetic NaN" }
>  print *, (2.0,-4.3)**(-huge(0)) ! { dg-error "Arithmetic NaN" }
>
> I.e. it expects a NaN for both cases.  What I'm getting with MPC is
> "Arithmetic overflow" on the first line because it overflows to Inf, and no
> error for the second presumably because it underflows to zero.
>
> I think perhaps expecting a NaN here is bogus and is an artifact of the
> hand-written algorithm chosen to evaluate complex**int inside the fortran
> frontend.  The code is in fortran/arith.c:complex_pow().  I suspect the
> algorithm is getting confused somewhere along the way.

I agree with everything you say, but I'd like to point out that one 
thing you should make sure is, that compiled code (or code generated by 
the optimizers) and code evaluated by the frontend yield the same 
results, i.e.

FUNCTION f(z, e)
 complex :: f, z, e
 f = z**e
END

PRINT *, f((2.0, -4.3), huge(0))
END

should behave the same.  With gfortran 4.1.2 this prints NaN.

Cheers,
- Tobi