Dear Jeff,

typedef struct { uint64_t context; uint64_t pointer; } MPI_Aint;

Is that incorrect?

I expect, that it is not correct. My apologies for that. In MPI-1.0 - MPI-2.1 all address calculation had to be done with - and + operators. Only for the case, that somebody switches integer overflow detection on, we added MPI_Aint_add and MPI_Aint_diff. We asked ourself, whether we want to deprecate the use of + and - operators, i.e., to add this to Table 2.1 on page 18 and the forum decided "no" per straw vote. We definitely never removed the operators + and - from the list of valid operations for MPI_Aint. MPI-3.1 on page 17 lines 16-18 clearly tells that any int, MPI:Aint, and MPI_Offset value can be assigned to a MPI_Count variable, i.e., all 4 must be integers of some byte-size. Best regards Rolf ----- Original Message -----

From: "Jeff Squyres" <[email protected]> To: "Rolf Rabenseifner" <[email protected]>, "mpiwg-large-counts" <[email protected]> Sent: Wednesday, October 23, 2019 4:19:53 PM Subject: Re: [Mpiwg-large-counts] Large Count - the principles for counts, sizes, and byte and nonbyte displacements

On Oct 9, 2019, at 1:44 PM, Rolf Rabenseifner via mpiwg-large-counts <[email protected]> wrote:

...

I never said that that a number is a displacement. MPI_Aint is clearly used for - addresses relative to a buffer begin, - absolute addresses (returned by MPI_GET_ADDRESS) - number of bytes.

MPI-3.1 says 2.5.6 Absolute Addresses and Relative Address Displacements Some MPI procedures use address arguments that represent an absolute address in the calling program, or relative displacement arguments that represent differences of two absolute addresses. The datatype of such arguments is MPI_Aint in C and INTEGER (KIND= MPI_ADDRESS_KIND) in Fortran.

I thought the whole point of MPI_Aint was to support segmented address spaces. Indeed, the next sentence in MPI-3.1 states:

"These types must have the same width and encode address values in the same manner such that address values in one language may be passed directly to another language without conversion."

This says to me that MPI_Aint can be encoded, which I take to mean the following:

1. This is exactly the reason why we have MPI_AINT_ADD / MPI_AINT_DIFF. 2. Presuming I have an MPI_ADDRESS_KIND value in Fortran that represents a 128 bit integer, the following is valid in C:

typedef struct { uint64_t context; uint64_t pointer; } MPI_Aint;

Is that incorrect?

-- Jeff Squyres [email protected]

-- Dr. Rolf Rabenseifner . . . . . . . . . .. email [email protected] . High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 . University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 . Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner . Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) .