[Bug middle-end/30789] complex folding inexact

["ghazi at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #3 from ghazi at gcc dot gnu dot org  2009-08-12 22:28 -------
(In reply to comment #2)

Joseph - Thanks for your reply and testvalues.

> There are also cases for exact rounding where you'd expect MPC to produce 
> the right results but would *not* expect operations executed at runtime to 
> produce exactly those results.  For example, (1.0 + DBL_EPSILON + 1.0i) * 
> (1.0 - DBL_EPSILON + 1.0i), which would only work at runtime if the code 
> happens to use exactly the right fused multiply-add operation.

What is the "right result" for this case?  GCC with MPC produces:
-4.93038065763132378382330353301741393545754021943139377981e-32 + 2.0i)

Unpatched GCC as well as the runtime on my x86_64 box says:
0.0 + 2.0i

So the runtime here is not using the fused instruction?

Is the MPC value correct?

Thanks.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30789