[petsc-dev] PETSc in double-double and quad-double...

[Kai Germaschewski]

gmp is part of macports, so it's as easy as "port install gmp" here.

If you want to put it into petsc's build system, looking at the macports
portfile / patches will probably reveal what's necessary to "port" it.

--Kai


On Fri, Jan 8, 2010 at 9:56 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>  I'm giving up on this for now. Building BlasLapack from the f or f2c
> source code of BlasLapack with qd is hopeless. So one could use mpack, but
> mpack requires gmp to build, but I am unable to build gmp on my Mac because
> it is not as portable as it is suppose to be.
>
>   There is a config/PETSc/packages/qd.py gmp.py and mpack.py if anyone
> wants to see if they can get the pieces built. Note: you will need to get
> the tarballs yourself, they are not on the website. If you hack MPACK to get
> things running then please do it in an hg repository. You might be able to
> hack mpack so it does not need gmp to build but .....
>
>   Cool idea but I am so pissed at bullshit non-portable code that pretends
> to be portable I'm giving up!
>
>
>   Barry
>
>
> On Nov 4, 2009, at 2:27 PM, Matthew Knepley wrote:
>
>  On Wed, Nov 4, 2009 at 2:21 PM, Jed Brown <jed at 59a2.org> wrote:
>> Matthew Knepley wrote:
>> > On Wed, Nov 4, 2009 at 2:06 PM, Barry Smith <bsmith at mcs.anl.gov
>> > <mailto:bsmith at mcs.anl.gov>> wrote:
>> >
>> >
>> >       This is tricky because some C/C++ compilers long double uses 128
>> >     bits of space but actually (on Intel) only uses 80 of the bits
>> >     (those are the bits that floating point unit handles). So you do not
>> >     really get 128 bits. Also MPI may not properly handle the 128 bit
>> >     doubles.
>> >
>> >
>> > I figured that his types were just C++ types once he said they were
>> > provided by a package.
>>
>> QD is honest quad-double (32 bytes, all of them significant)
>>
>>  http://crd.lbl.gov/~dhbailey/mpdist/<http://crd.lbl.gov/%7Edhbailey/mpdist/>
>>
>> They are C++ types with appropriate overloading, but the operations are
>> implemented in terms of conventional double-precision where as "long
>> double" is a different beast.
>>
>> Okay, then this should be no harder than complex.
>>
>> >       I am investigating qd now. Is there any MPI implementation that
>> >     uses qd? Do you need MPI?
>> >
>> >
>> > Can't we just make a type the correct number of bytes long?
>>
>> I think so (on homogeneous hardware), but you have to create your own
>> version of each MPI_Op that does the right thing with this longer type.
>>
>> Yep, we do that now for several things in PETSc.
>>
>>  Matt
>>
>> Jed
>>
>>
>>
>>
>> --
>> What most experimenters take for granted before they begin their
>> experiments is infinitely more interesting than any results to which their
>> experiments lead.
>> -- Norbert Wiener
>>
>
>


-- 
Kai Germaschewski
Assistant Professor, Dept of Physics / Space Science Center
University of New Hampshire, Durham, NH 03824
office: Morse Hall 245F
phone:  +1-603-862-2912
fax: +1-603-862-2771
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