[Bug c/24581] Complex arithmetic on special cases is incorrect.

["joseph at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #1 from joseph at codesourcery dot com  2005-10-29 20:09 -------
Subject: Re:   New: Complex arithmetic on special cases is
 incorrect.

On Sat, 29 Oct 2005, kargl at gcc dot gnu dot org 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.

I suspect there are lots of presumptions in the compiler that arithmetic 
operations such as PLUS_EXPR and MULT_EXPR have both operands of the same 
type, which would need to be fixed to represent a real*complex product 
properly.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24581