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[Bug c/24581] Complex arithmetic on special cases is incorrect.
- From: "sgk at troutmask dot apl dot washington dot edu" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 29 Oct 2005 20:27:14 -0000
- Subject: [Bug c/24581] Complex arithmetic on special cases is incorrect.
- References: <bug-24581-10110@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #4 from sgk at troutmask dot apl dot washington dot edu 2005-10-29 20:27 -------
Subject: Re: Complex arithmetic on special cases is incorrect.
On Sat, Oct 29, 2005 at 08:09:45PM -0000, joseph at codesourcery dot com wrote:
>
> > * underflow, sign and efficiency bugs by rewriting I*y as
> > * (0.0+I)*(y+0.0*I) and laboriously computing the full complex product.
>
> Note that the correct form is (0.0+I)*y, since I is (per C99+TC1+TC2)
> _Complex_I, of complex type (Annex G imaginary types conflicting with the
> normative standard, unless and until anything changes in this respect
> following DR#323). But the usual arithmetic conversions as specified in
> the standard do not convert both operands to complex, so one can be real
> and one complex.
>
If I read Annex G correctly, the z = I*inf = NaN + I inf
is going to really bad things because the NaN is going to
propagate if z is used in further computations. Annex G
says z is an infinity.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24581