[mpich-discuss] Fortran integer support 4/8-bytes

[Jed Brown]

On Thu, Jun 7, 2012 at 6:55 PM, William Gropp <wgropp at illinois.edu> wrote:

> Note that there is no reason that the C compiler couldn't use 8 bytes for
> an int;


But this would change the data model so the compiler can't change this at
will without breaking binary compatibility with libc and the rest of the
system.

You could in principle build up an entire operating system (starting with
libc) using an ILP64 data model (though even GCC does not support this
option for most architectures), but you would be adopting/defining an
unsupported ABI.

(Unicos was SILP64 and apparently HAL's port of Solaris to SPARC64 was
ILP64, so (S)ILP64 has been supported by some vendors, but it's far from
mainstream.)
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