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Re: [PATCH] Update x86_64 ULPs
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: OndÅej BÃlka <neleai at seznam dot cz>
- Cc: Carlos O'Donell <carlos at redhat dot com>, Andreas Jaeger <aj at suse dot com>, Markus Trippelsdorf <markus at trippelsdorf dot de>, <libc-alpha at sourceware dot org>
- Date: Thu, 2 May 2013 20:34:46 +0000
- Subject: Re: [PATCH] Update x86_64 ULPs
- References: <20130426055835 dot GA644 at x4> <517A2CF9 dot 20504 at suse dot com> <20130502160937 dot GA8564 at domone dot kolej dot mff dot cuni dot cz> <Pine dot LNX dot 4 dot 64 dot 1305021847100 dot 12072 at digraph dot polyomino dot org dot uk> <5182B698 dot 20501 at redhat dot com> <20130502202953 dot GA13508 at domone dot kolej dot mff dot cuni dot cz>
On Thu, 2 May 2013, Ondrej Bilka wrote:
> On Thu, May 02, 2013 at 02:55:20PM -0400, Carlos O'Donell wrote:
> > On 05/02/2013 02:49 PM, Joseph S. Myers wrote:
> > > On Thu, 2 May 2013, Ondrej Bilka wrote:
> > >
> > >> Could we compute ulp directly with mpfr or I am missing some roadblock?
> > >
> > > The whole point of ulps baselines is to record the errors produced by the
> > > actual glibc implementation, compared to an exact expected result (which
> > > quite likely was computed with MPFR). Those baselines can, on x86 and
> > > x86_64, depend on the processor implementation of the x87 instructions for
> > > transcendental operations (so on whether an Intel or AMD processor is in
> > > use, for example), as well as, on 32-bit x86, on the details of where the
> > > compiler uses excess precision.
> > >
>
> So mpfr computations depend on processor used?
No. The difference between the exact result from MPFR, and the actual
result from libm, depends on the actual result from libm, which depends on
the processor used. And the point of libm-test-ulps is to record the
maximum expected values of those differences on each platform.
--
Joseph S. Myers
joseph@codesourcery.com