[OMPI users] Use of __float128 with openmpi
Hi all, I have a question on datatypes in openmpi: Is there an (easy?) way to use __float128 variables with openmpi? Specifically, functions like MPI_Allreduce seem to give weird results with __float128. Essentially all I found was http://beige.ucs.indiana.edu/I590/node100.html where they state MPI_LONG_DOUBLE This is a quadruple precision, 128-bit long floating point number. But as far as I have seen, MPI_LONG_DOUBLE is only used for long doubles. The Open MPI Version is 1.6.3 and gcc is 4.7.3 on a x86_64 machine. Any help or comment is very appreciated! Best regards, Patrick
Re: [OMPI users] Use of __float128 with openmpi
Hello Jeff,
thank you a lot for your reply!
On 01.02.2014, at 23:07, Jeff Hammond wrote:
> See Section 5.9.5 of MPI-3 or the section named "User-Defined
> Reduction Operations" but presumably numbered differently in older
> copies of the MPI standard.
>
> An older but still relevant online reference is
> http://www.mpi-forum.org/docs/mpi-2.2/mpi22-report/node107.htm
>
In this example they construct this "datatype"
-
typedef struct {
double real,imag;
} Complex
-
and later
-
MPI_Datatype ctype;
/* explain to MPI how type Complex is defined
*/
MPI_Type_contiguous(2, MPI_DOUBLE, &ctype);
-
Do I understand correctly that I have to find out how __float128 is constructed
internally and
convert it to a form which is compatible with the standard MPI Datatypes?
In an analogue way as they do in the example. Up to now, I only found out that
__float128 should
be somehow the sum of two doubles.
Again, I am grateful for any help!
Best regards,
Patrick
> On Sat, Feb 1, 2014 at 2:28 PM, Tim Prince wrote:
>>
>> On 02/01/2014 12:42 PM, Patrick Boehl wrote:
>>>
>>> Hi all,
>>>
>>> I have a question on datatypes in openmpi:
>>>
>>> Is there an (easy?) way to use __float128 variables with openmpi?
>>>
>>> Specifically, functions like
>>>
>>> MPI_Allreduce
>>>
>>> seem to give weird results with __float128.
>>>
>>> Essentially all I found was
>>>
>>> http://beige.ucs.indiana.edu/I590/node100.html
>>>
>>> where they state
>>>
>>> MPI_LONG_DOUBLE
>>> This is a quadruple precision, 128-bit long floating point number.
>>>
>>>
>>> But as far as I have seen, MPI_LONG_DOUBLE is only used for long doubles.
>>>
>>> The Open MPI Version is 1.6.3 and gcc is 4.7.3 on a x86_64 machine.
>>>
>> It seems unlikely that 10 year old course notes on an unspecified MPI
>> implementation (hinted to be IBM power3) would deal with specific details of
>> openmpi on a different architecture.
>> Where openmpi refers to "portable C types" I would take long double to be
>> the 80-bit hardware format you would have in a standard build of gcc for
>> x86_64. You should be able to gain some insight by examining your openmpi
>> build logs to see if it builds for both __float80 and __float128 (or
>> neither). gfortran has a 128-bit data type (software floating point
>> real(16), corresponding to __float128); you should be able to see in the
>> build logs whether that data type was used.
>>
>>
>> ___
>> users mailing list
>> us...@open-mpi.org
>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
>
> --
> Jeff Hammond
> jeff.scie...@gmail.com
> ___
> users mailing list
> us...@open-mpi.org
> http://www.open-mpi.org/mailman/listinfo.cgi/users
Re: [OMPI users] Use of __float128 with openmpi
Hello Tim, thank you for your reply! On 01.02.2014, at 21:28, Tim Prince wrote: > Where openmpi refers to "portable C types" I would take long double to be the > 80-bit hardware format you would have in a standard build of gcc for x86_64. > You should be able to gain some insight by examining your openmpi build logs > to see if it builds for both __float80 and __float128 (or neither). Unfortunately, these are not my machines, so I do not have access to any build logs. But I will talk to the admins and/or I try to compile openmpi myself. Best regards, Patrick
Re: [OMPI users] Use of __float128 with openmpi
Hello George,
thank you a lot!
Everything seems to work now! :)
Best,
Patrick
On 02.02.2014, at 14:15, George Bosilca wrote:
> Just go for the most trivial:
>
> MPI_Type_contiguous(sizeof(__float128), MPI_BYTE, &my__float128);
>
> A little bit more info about the optional quad-precision floating-point
> format is available on Wikipedia
> (https://en.wikipedia.org/wiki/Double-double_%28arithmetic%29#Double-double_arithmetic).
>
> George.
>
>
> On Feb 2, 2014, at 13:41 , Patrick Boehl
> wrote:
>
>> Hello Jeff,
>>
>> thank you a lot for your reply!
>>
>> On 01.02.2014, at 23:07, Jeff Hammond wrote:
>>
>>> See Section 5.9.5 of MPI-3 or the section named "User-Defined
>>> Reduction Operations" but presumably numbered differently in older
>>> copies of the MPI standard.
>>>
>>> An older but still relevant online reference is
>>> http://www.mpi-forum.org/docs/mpi-2.2/mpi22-report/node107.htm
>>>
>>
>> In this example they construct this "datatype"
>>
>> -
>> typedef struct {
>> double real,imag;
>> } Complex
>> -
>>
>> and later
>>
>> -
>> MPI_Datatype ctype;
>> /* explain to MPI how type Complex is defined
>> */
>> MPI_Type_contiguous(2, MPI_DOUBLE, &ctype);
>> -
>>
>> Do I understand correctly that I have to find out how __float128 is
>> constructed internally and
>> convert it to a form which is compatible with the standard MPI Datatypes?
>> In an analogue way as they do in the example. Up to now, I only found out
>> that __float128 should
>> be somehow the sum of two doubles.
>>
>> Again, I am grateful for any help!
>>
>> Best regards,
>> Patrick
>>
>>
>>
>>
>>> On Sat, Feb 1, 2014 at 2:28 PM, Tim Prince wrote:
>>>>
>>>> On 02/01/2014 12:42 PM, Patrick Boehl wrote:
>>>>>
>>>>> Hi all,
>>>>>
>>>>> I have a question on datatypes in openmpi:
>>>>>
>>>>> Is there an (easy?) way to use __float128 variables with openmpi?
>>>>>
>>>>> Specifically, functions like
>>>>>
>>>>> MPI_Allreduce
>>>>>
>>>>> seem to give weird results with __float128.
>>>>>
>>>>> Essentially all I found was
>>>>>
>>>>> http://beige.ucs.indiana.edu/I590/node100.html
>>>>>
>>>>> where they state
>>>>>
>>>>> MPI_LONG_DOUBLE
>>>>> This is a quadruple precision, 128-bit long floating point number.
>>>>>
>>>>>
>>>>> But as far as I have seen, MPI_LONG_DOUBLE is only used for long doubles.
>>>>>
>>>>> The Open MPI Version is 1.6.3 and gcc is 4.7.3 on a x86_64 machine.
>>>>>
>>>> It seems unlikely that 10 year old course notes on an unspecified MPI
>>>> implementation (hinted to be IBM power3) would deal with specific details
>>>> of
>>>> openmpi on a different architecture.
>>>> Where openmpi refers to "portable C types" I would take long double to be
>>>> the 80-bit hardware format you would have in a standard build of gcc for
>>>> x86_64. You should be able to gain some insight by examining your openmpi
>>>> build logs to see if it builds for both __float80 and __float128 (or
>>>> neither). gfortran has a 128-bit data type (software floating point
>>>> real(16), corresponding to __float128); you should be able to see in the
>>>> build logs whether that data type was used.
>>>>
>>>>
>>>> ___
>>>> users mailing list
>>>> us...@open-mpi.org
>>>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>>
>>>
>>>
>>> --
>>> Jeff Hammond
>>> jeff.scie...@gmail.com
>>> ___
>>> users mailing list
>>> us...@open-mpi.org
>>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>
>> ___
>> users mailing list
>> us...@open-mpi.org
>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
> ___
> users mailing list
> us...@open-mpi.org
> http://www.open-mpi.org/mailman/listinfo.cgi/users
