The short answer is yes. However, this answer is wrong in a heterogeneous environment. Suppose one rank is a 32 bits process, and the size_t is 4 bytes, while another one is 64 bits with a size_t of 8 bytes. If you correlate the sizeof(size_t) with the type you use for a communication, then one process will use MPI_UINT32_T while the other MPI_UINT64_t. Based on the typemap matching rules defined by MPI, there will be no automatic (MPI-based) conversion between these two types.
I'm just pointing out that the portability in MPI is sometimes not as straightforward as one might assume. George. On Mar 14, 2013, at 15:09 , Gus Correa <g...@ldeo.columbia.edu> wrote: > Many thanks, George! > > I passed MPI_AINT to the MPI functions, > along with the ptrdiff_t buffers, > and it worked right, at least for the modest > buffer sizes I tried. > > I haven't got to size_t buffers yet, but if I understood right, > your suggestion for size_t buffers would be to > use MPI_UINT64_T as MPI data type on 64-bit machines, right? > [Probably MPI_UINT32_T on 32-bit, I presume.] > > Thank you, > Gus Correa > > On 03/13/2013 07:42 PM, George Bosilca wrote: >> MPI_Aint is always signed, as it is supposed to be able to > hold any relative difference between two memory locations. > This it is a good match for ptrdiff_t. >> >> There is no direct match for size_t, at least not > directly exposed by the MPI standard > (using the MPI-2.2 POSIX types, e.g MPI_UINT64_T). > My understanding is that size_t is unsigned, > and ssize_t is the signed synonym. >> >> George. >> >> >> On Mar 13, 2013, at 23:30 , Gus Correa<g...@ldeo.columbia.edu> wrote: >> >>> Dear Open MPI Pros >>> >>> Which MPI data type corresponds to ptrdiff_t in C? >>> I guess the same question can be asked about size_t. >>> >>> The FFTW3.3 MPI API has lots of stuff declared as >>> ptrdiff_t, and I need to pass them around with MPI, >>> hopefully without size or sign mistakes. >>> >>> I am using Open MPI 1.6.3, if this matters. >>> My C goes as far as ABC, and in my naive view >>> ptrdiff_t is signed and has 64-bits on my x86_64 Linux computer, >>> whereas size_t is unsigned also 64-bits, right? >>> >>> If I grep mpi.h for ptrdiff I see that OPAL_PTRDIFF_TYPE is >>> MPI_Aint, which is indeed an MPI pointer/address type. >>> However, this is OPAL, not generic MPI. >>> Moreover, MPI_Aint seems to be unsigned, right? >>> [And this would make it a bad match for ptrdiff_t, >>> but maybe a good match for size_t.] >>> Or is MPI_Aint signed? >>> >>> [grep result:] >>> 147:/* type to use for ptrdiff_t, if it does not exist, set to ptrdiff_t if >>> it does exist */ >>> 148:#define OPAL_PTRDIFF_TYPE ptrdiff_t >>> 218:/* include for ptrdiff_t */ >>> 317:typedef OPAL_PTRDIFF_TYPE MPI_Aint; >>> >>> OTOH, there are bunches of signed and unsigned integer MPI types >>> in mpi.h. >>> In a 64-bit machine, besides MPI_Aint, >>> I guess possible candidates would be >>> MPI_INT64_T and MPI_UINT64_T. >>> But which one: signed or unsigned? >>> >>> Even if I write a little function to find an MPI integer type >>> with the same extent as sizeof(ptrdiff_t), it may still >>> return more than one type, and be problematic to pick one >>> (e.g., signed or unsigned?). >>> >>> Any help is appreciated. >>> Gus Correa >>> _______________________________________________ >>> 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
