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MPI_Type_create_f90_integer

MPI_Type_create_f90_integer - Returns a bounded MPI integer datatype

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Type_create_f90_integer(int r, MPI_Datatype *newtype)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_TYPE_CREATE_F90_INTEGER (R, NEWTYPE, IERROR)
     INTEGER R, NEWTYPE, IERROR

Fortran 2008 Syntax

USE mpi_f08
MPI_Type_create_f90_integer(r, newtype, ierror)
     INTEGER, INTENT(IN) :: r
     TYPE(MPI_Datatype), INTENT(OUT) :: newtype
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETER

  • r: Precision, in decimal digits (integer).

OUTPUT PARAMETERS

  • newtype: New data type (handle).
  • ierror: Fortran only: Error status (integer).

DESCRIPTION

This function provides a way to declare KIND-parameterized INTEGER MPI datatypes. The argument is interpreted in a similar fashion to the F90 function SELECTED_INT_KIND: r must be a scalar integer, and represents the desired level of numerical precision, in decimal digits.

NOTES

It is erroneous to supply a value for r not supported by the compiler.

The Fortran function SELECTED_INT_KIND maps a large number of r values to a much smaller number of KIND parameters supported by the compiler. KIND parameters are not specified by the language and are not portable. From the point of view of the language, variables of the same base type and KIND parameter are equivalent, even if their KIND parameters were generated by different r arguments to SELECTED_INT_KIND. However, to help facilitate interoperability in a heterogeneous environment, equivalency is more strictly defined for datatypes returned by :ref:`MPI_Type_create_f90_integer`. Two MPI datatypes, each generated by this function, will match if and only if they have identical values for r.

The interaction between the datatypes returned by this function and the external32 data representation - used by :ref:`MPI_Pack_external`, :ref:`MPI_Unpack_external` and many MPI_File functions - is subtle. The external32 representation of returned datatypes is as follows.

if (r > 38):
        external32 size = n/a (undefined)
else if (r > 18):
        external32 size = 16
else if (r > 9):
        external32 size = 8
else if (r > 4):
        external32 size = 4
else if (r > 2):
        external32 size = 2
else:
        external32 size = 1

If the external32 representation of a datatype is undefined, so are the results of using that datatype in operations that require the external32 format. Care should be taken not to use incompatible datatypes indirectly, e.g., as part of another datatype or through a duplicated datatype, in these functions.

If a variable is declared specifying a nondefault KIND value that was not obtained with SELECTED_INT_KIND (i.e., r is unknown), the only way to obtain a matching MPI datatype is to use the functions :ref:`MPI_Sizeof` and :ref:`MPI_Type_match_size`.

ERRORS

.. seealso::
   * :ref:`MPI_Pack_external`
   * :ref:`MPI_Sizeof`
   * :ref:`MPI_Type_match_size`
   * :ref:`MPI_Unpack_external`
   * SELECTED_INT_KIND