[Mpi-forum] large count support not as easy as people seem to have thought

Jed Brown jedbrown at mcs.anl.gov
Tue May 6 16:46:20 CDT 2014

Rob Latham <robl at mcs.anl.gov> writes:
> i imagine one day (once again?) the c int type will be 64 bits on a 
> platform, right?
> or will c ints be 32 bits for ever?

2^64 is quite a lot of memory.  The popular 64-bit systems use LP64 or
LLP64, both of which have 32-bit ints.  I don't foresee any major player
having incentive to promote int to 64-bits.  I think it's worth fixing
this interface problem _and_ fixing the MPI_Op support so that libraries
can build robust abstractions.  (I have example use cases in PETSc that
caused a bit of discussion including the creation of ticket #338, and
now Jeff has another.)
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