Date: Mon, 22 Oct 2012 07:38:28 -0600 From: Warner Losh <imp@bsdimp.com> To: Bruce Evans <brde@optusnet.com.au> Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org, Warner Losh <imp@FreeBSD.org> Subject: Re: svn commit: r241755 - head/lib/msun/src Message-ID: <80A9038D-C84B-47D3-A137-F281449F4D88@bsdimp.com> In-Reply-To: <20121022213348.T1373@besplex.bde.org> References: <201210192246.q9JMkm4R092929@svn.freebsd.org> <20121020150917.I1095@besplex.bde.org> <18177777-6EE0-4103-98B0-272EFF98FE96@bsdimp.com> <20121022213348.T1373@besplex.bde.org>
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On Oct 22, 2012, at 5:14 AM, Bruce Evans wrote:
> On Sun, 21 Oct 2012, Warner Losh wrote:
>=20
>> Feel free to fix them however. I added the comments because the =
algorithms weren't quite the same... If you have a better way, feel =
free to back my stuff out on the way to it.
>=20
> But the algorithms are identical to a fault. Inside the functions, =
all
> lines except 1 in each correspond exactly, and the exception is a =
style
> bug. Only about 30 lines in each are not lexically identical. The
> non-lexical differences are for things like different magic numbers.
Except that's not true. For expf, only the first two terms of the 5 are =
computed in Remes expansion. That's why I bothered to document the =
difference. For logf, there are at least two additional terms in the =
intermediate form.
The differences here are:
/* logf */
t1=3D w*(Lg2+w*Lg4);=20
t2=3D z*(Lg1+w*Lg3);=20
/* log */
t1=3D w*(Lg2+w*(Lg4+w*Lg6));
t2=3D z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
=20
which to even the most casual observer are clearly different.
> The old fdlibm comments aren't too careful about keeping magic numbers
> out of the algorithm description so that the algorithm description is
> as general as possible. The precise magic numbers are often critical
> to the details of the implementation of the algorithm but not really
> to the algorithm itself.
The current code isn't careful at all about magic numbers. Which ones =
are magic hex constants for IEEE stuff, and which ones are hex numbers =
for the exact representation of important constants?
Anyway, it is clear you guys don't want them in there so I've reverted =
them. I'm totally baffled by this request because these algorithms are =
similar not identical, but since you guys are the active maintainers, =
I'll accede to your wishes after expressing my utter bafflement at the =
justifications.
Warner=
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