Date: Thu, 31 May 2012 12:12:16 -0500 From: Stephen Montgomery-Smith <stephen@missouri.edu> To: freebsd-current@freebsd.org Subject: Re: Use of C99 extra long double math functions after r236148 Message-ID: <4FC7A670.40004@missouri.edu> In-Reply-To: <201205311145.15454.jhb@freebsd.org> References: <4FC30090.4070003@gwdg.de> <20120528210507.GF2675@aspire.rulingia.com> <20120528230218.GC76723@troutmask.apl.washington.edu> <201205311145.15454.jhb@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On 05/31/12 10:45, John Baldwin wrote:
> On Monday, May 28, 2012 7:02:18 pm Steve Kargl wrote:
>> On Tue, May 29, 2012 at 07:05:07AM +1000, Peter Jeremy wrote:
>>> On 2012-May-28 11:01:24 -0500, Stephen Montgomery-Smith
> <stephen@missouri.edu> wrote:
>>>> One thing that could be done is to have a "math/cephes" port that adds
>>>> the extra C99 math functions. This is already done in the math/sage
>>>> port, using a rather clever patch due to Peter Jeremy, that applies to
>>>> the cephes code.
>>>>
>>>> What it would do is to create a /usr/local/lib/libm.so that would
>>>> provide the extra functions not currently included in /lib/libm.so, and
>>>> then link in /lib/libm.so as well. It would also create its own
>>>> /usr/local/include/math.h and /usr/local/include/complex.h as well.
>>>
>>> Basically, as long as the compiler searches /usr/local/{include,lib}
>>> before the base include/lib then<math.h>,<complex.h> and -lm give
>>> the application a complete C99 math implementation by using base
>>> functions where they exist and cephes functions where they don't.
>>>
>>> The patch I wrote for sage can be found at
>>> http://trac.sagemath.org/sage_trac/ticket/9543
>>> If there's any interest, I could produce a port for this.
>>>
>>> Another option would be to import cephes into base and use it to
>>> provide the missing C99 functions. Cephes includes copyright notices
>>> but the closest I can find to a license is:
>>> " Some software in this archive may be from the book _Methods and
>>> Programs for Mathematical Functions_ (Prentice-Hall or Simon& Schuster
>>> International, 1989) or from the Cephes Mathematical Library, a
>>> commercial product. In either event, it is copyrighted by the author.
>>> What you see here may be used freely but it comes with no support or
>>> guarantee."
>>
>> Please talk to das@ (although I believe he's finishing up his
>> dissertation). I recall that he's stated that he looked into
>> using cephes, and concluded that it is not suitable for libm.
>>
>> Note there is also
>>
>> http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/147599
>>
>> which I've also objected to importing into libm.
>
> I do think we should provide something in ports as an interim solution.
> There are other 3rd party applications looking to drop FreeBSD support
> because we are missing APIs that almost all other OS's have. I'm fine
> if the interim lives in ports and that we don't import substandard
> routines into the base. I would even be fine with calling it
> /usr/local/lib/libm_inaccurate.so. However, I do think we need an option.
>
I think it should be called libm.so. Otherwise we have to do a serious
editing job on the Makefiles/configure scripts.
sed -E 's/[[:<:]]-lm[[:>:]]/-lm_inaccuarate/'
might have some false positives and false negatives. (Did I even get
the sed syntax correct?)
By the way, I was looking through:
http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/147599
They say they compute cosh(2y) - cos(2x) using Taylor's series. I would
agree with Steve that this is seriously low quality. Floating point
errors are likely to be truly horrible. This will fail even for
non-edge cases. (This was the same error that openoffice used to have
for computing erf(x), that gave things like erf(100) = -4353243242.)
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?4FC7A670.40004>