Re: [Patch, fortran] PR24518 - Intrinsic MOD incorrect for large arg1/arg2 and slow.

[Steve Kargl <sgk at troutmask dot apl dot washington dot edu>]

On Wed, Nov 01, 2006 at 02:49:34PM -0700, Roger Sayle wrote:
> Hi Uros and Paul,
> On Wed, 1 Nov 2006, Paul Thomas wrote:
> > >> Regtested on FC5/x86_ia64 - OK for trunk, and 4.2?
> > >
> > > In 4.2, the fmod intrinsic is still protected by
> > > flag_unsafe_math_optimizations. For your fortran patch to be effective
> > > on 4.2, fmod patch
> > > (http://gcc.gnu.org/ml/gcc-patches/2006-10/msg01209.html) needs to be
> > > backported to 4.2. [Patch was OK'd for mainline].
> > >
> > > Roger, is fmod patch also OK for 4.2?
> > >
> > > Ah yes, you are quite right.  This is not exactly a bug fix, is it?
> > > OK for trunk, then? :-)
> 
> I believe Paul's patch should be suitable for 4.2, for two reasons.
> Firstly, the poor numerical accuracy of gfortran's MOD and MODULO is a
> regression from g77 (indeed I've just confirmed this with g77 from
> gcc-3.4.3 using a slightly tweaked version of the test case given in:
> http://gcc.gnu.org/ml/gcc-patches/2006-10/msg01741.html
> 
> Secondly, I believe Paul's patch is fine even without Uros' x87 intrinsic
> patch.  Adding support for inlining fmod calls on IA-32 clearly helps
> performance-wise [on one particular target], but isn't a blocker for
> correctness, where we'll simply call libm's fmod, as we do on other
> platforms.  [Should anywhere not have fmod, it's simple enough to
> cook something up for libgfortran/intrinsics/c99_functions.c].
> 
> Does this sound like a reasonable compromise?

Yes, it seems reasonable to me.

-- 
Steve