[Bug target/60181] constant folding of complex number incorrect

[joseph at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60181

--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
There are no specified accuracy requirements for complex multiplication / 
division, even under Annex G (parts of which - imaginary types in 
particular - are not implemented in GCC at present), beyond certain 
requirements for special cases and avoiding certain cases of overflow from 
the simplest formulas.  Constant folding is correctly rounding, runtime 
complex multiplication / division isn't (and given complaints about 
slowness at present, I don't think users would want it to be even slower, 
though there may well be a case for defining a standard library interface 
for correctly rounding complex multiplication / division).

x86 probably benefits from excess precision being used implicitly by GCC 
when compiling the implementations of complex multiplication and division.