It does this for systems that allow the use to change the lengths of the basic types in Fortran.  This is a (IMHO) terrible hack, but quite a few applications use it.  MPICH makes this change *only* when it knows that DOUBLE PRECISION  is the same size as REAL*8 .  This makes a difference on IBM systems, for example, where the xl compiler has an option to change the size of DOUBLE PRECISION, but that option does not change the size of explicit-sized types such as REAL*8.

Bill

On Feb 12, 2010, at 3:47 PM, Kiryanov, Yury wrote:

Hello,
 
Could you explain why configure substitutes the ‘DOUBLE PRECISION’ to ‘REAL*8’ declaration of MPI_WTIME, MPI_WTICK into mpif.h and mpi_base.f90?
It has been changed into mpich2-1.0.8. I’m asking about it because the MPI-2 says that it should be declared as DOUBLE PRECISION.
 
Thank you.
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Best regards,
Yury Kiryanov
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