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Re: Update x86 ulps for GCC 7 [committed]
On 2017.06.26 at 10:43 +0000, Joseph Myers wrote:
> On Sat, 24 Jun 2017, Markus Trippelsdorf wrote:
> > On 2017.06.23 at 20:23 +0000, Joseph Myers wrote:
> > > Testing with GCC 7 for 32-bit x86 showed some ulps differences,
> > > presumably from variation in when values with excess precision get
> > > spilled to the stack and so lose that precision. This patch updates
> > > the libm-test-ulps files accordingly.
> > For AMD Ryzen x86_64 I need an additional update:
> Such updates should generally just be committed. In this case (x86_64,
> not long double) I'm not clear why you'd have ulps variation between
> processors, since excess precision is irrelevant on x86_64 and the x87
> transcendental instructions would only be used for long double. But it
> could be an fma issue, if $CC $CFLAGS defaults to generating fma
> instructions, as that can cause ulps variation across architectures.
Yes, it should be an fma issue because I used "march=native" (which
turns on -mfma).
I don't have write access, so it would be nice if somebody could commit
the patch for me.