This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [PATCH]: PR29335 use MPFR for two-argument math builtins (pow, atan2, hypot)


On Sat, 28 Oct 2006, Bradley Lucier wrote:
>  > hypot(x,x) -> x*sqrt(2)
>
> I think this can change the value computed in some cases, because
> there's one rounding error computing sqrt(2) and one more computing
> the multiplication.

Grr.  I missed this.  I did give some thought to multiple rounding
when reviewing the patch, but I made the (obvious in retrospect)
incorrect assumption that the compile-time constant sqrt(2) wasn't
rounded, so the perfect rounding of the single multiplication was
acceptable.  Alas not.

Kaveh, I'll preapprove the "obvious" simple change to control this
transformation with flag_unsafe_math_optimizations.

Many thanks to Brad for catching this.

Roger
--


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]