MPICount

MPICount is a term encountered in MPI (Message Passing Interface) programming used to describe a numeric counter corresponding to the number of elements or displacements involved in MPI operations. It is not an official MPI datatype or keyword in the standard, but rather represents the conceptual role of a large counter in communications and data handling. In discussions and code, MPICount is often used interchangeably with references to large-count concepts enabled by the MPI ecosystem.

In the MPI standard, the formal mechanism for representing counts that may exceed 32-bit limits is MPI_Count. Introduced with MPI-3 and maintained in later versions, MPI_Count is a signed integer type designed to hold counts of elements across operations, helping to prevent overflow in large-scale computations. On common platforms, MPI_Count maps to 64-bit (or wider) integer types, and it is used in contexts where counts or displacements need to be expressed beyond the capacity of standard int types.

Usage and portability considerations: MPICount as a programming alias or variable name is not a portable MPI construct. For portability and clarity, developers should rely on MPI_Count when a function or API explicitly supports it, and consult the specific MPI implementation documentation for details about which routines accept MPI_Count versus int. Many legacy MPI calls continue to use int for counts, so wrappers or extensions may introduce MPICount as a semantic alias in higher-level code.

See also: MPI, MPI_Count, MPI_Aint, large-count support in MPI, MPI-3.