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Date:	Wed, 21 Apr 2010 21:20:58 +0200
From:	Reini Urban <rurban AT x-ray DOT at>
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Subject:	Re: Cygwin Perl and -Duselongdouble
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Yitzchak Scott-Thoennes schrieb:
> On Thu, July 26, 2007 5:19 am, Corinna Vinschen wrote:
>> On Jul 26 22:09, Sisyphus wrote:
>>> I'd like to have a perl on Cygwin built with -Duselongdouble, so I tried
>
>>> *** You requested the use of long doubles but you do not seem to have
>>> *** the following mathematical functions needed for long double support:
>>>   ***     sqrtl modfl frexpl
>>
>> Long double functions are not supported by newlib so far.  There are a
>> couple of C99 functions not available in newlib.  Volunteers implementing
>> these functions in a license compatible way (BSD, not GPL) in newlib are
>> always welcome.
>
> Note that changing perl to use long doubles is a binary incompatible change.
> So if anyone is going to jump on this, it would be nice to have it happen
> before the already incompatible 5.10 is out Septemberish.
>
> modfl isn't strictly necessary; perl will substitute aintl (a solaris
> flavor of truncl) + copysignl.
> And ilogbl + scalbnl can be used to emulate frexpl.

I think I'll bite the bullet for the upcoming perl-5.12.0, for which I 
already have an API change (-Uusemymalloc) so adding -Duselongdouble can 
be easily added.

I dissected long doubles for my parrot pbc_compat work last year so I 
believe I can do modfl and frexpl without looking at GPL infected code.
http://code.google.com/p/cygwin-rurban/source/browse/trunk/release/parrot/patches/r36819-tt308-more-pf_items.patch

sqrtl is trivial in intel assembler:

long double sqrtl(long double ld) {
   long double _result;
   asm ("fsqrt" : "=t" (_result) : "0"(ld));
   return _result;
}

These questions are for newlib later:
Can I keep such a newlib code to 12-byte intel long doubles or must I 
add 16-byte long double support also?
Our gcc has -m128bit-long-double and the bastard -m96bit-long-double.
Does newlib needs papers?

I see a comment about --enable-newlib-hw-fp in
/usr/include/machine/ieeefp.h
I have no idea what this should be. Is there some hidden prior art?

I only know about Dave Korn's libm/machine/i386/f_*l.c stuff and I have 
newlib cvs.
-- 
Reini Urban
http://phpwiki.org/  http://murbreak.at/

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