From: Paul Zimmermann <Paul.Zimmermann@inria.fr>
To: Keith Packard <keithp@keithp.com>
Cc: newlib@sourceware.org
Subject: Re: issue with tgammaf
Date: Wed, 13 Jan 2021 08:52:39 +0100 [thread overview]
Message-ID: <mwpn29mfy0.fsf@tomate.loria.fr> (raw)
In-Reply-To: <87mtxdmjdd.fsf@keithp.com> (message from Keith Packard on Tue, 12 Jan 2021 22:38:38 -0800)
Dear Keith,
> Are you able to share the code which performs these tests? I'd love to
> be able to run these on a regular basis to ensure that no regressions
> occur as we maintain the code.
I will send you privately the code, since it is not yet ready for a wide
distribution.
> > tgamma:
> > Total: errors=2028164922 (47.41%) errors2=1833526367 maxerr=2.39e+02 ulp(s)
> > Total: errors=2026865970 (47.38%) errors2=1832940352 maxerr=2.39e+02 ulp(s)
>
> Given that around half of the possible input values (> 35, or near
> negative integers) generate an overflow, it seems like tgamma
> essentially *never* gives us an accurate finite result...
on a sample of 1/1000 of all values, it appears most errors come from exponents
(ilogbf) between -64 and -7. For example with exponent -64 I get no incorrect
rounding with glibc-2.32 out of 16776 samples, but 16410 with newlib.
For example for x=0x1.00e8p-64 newlib gives 0x1.fe31d6p+63 whereas the correct
rounding is 0x1.fe31a4p+63 according to MPFR.
Best regards,
Paul
next prev parent reply other threads:[~2021-01-13 7:52 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-15 8:21 Paul Zimmermann
2020-09-15 17:28 ` Keith Packard
2020-09-16 8:33 ` Paul Zimmermann
2020-09-16 15:13 ` Keith Packard
2020-09-17 7:18 ` Paul Zimmermann
2020-09-17 16:11 ` Keith Packard
2021-01-13 5:46 ` Paul Zimmermann
2021-01-13 6:38 ` Keith Packard
2021-01-13 7:52 ` Paul Zimmermann [this message]
2020-09-18 21:21 ` Jeff Johnston
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