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Re: 64 bit fortran unformatted on Opteron -- incompatible with32unformatted
- From: Bud Davis <bdavis at gcc dot gnu dot org>
- To: gcc-help at gcc dot gnu dot org
- Cc: Toon Moene <toon at moene dot indiv dot nluug dot nl>, gfortran <fortran at gcc dot gnu dot org>
- Date: Tue, 15 Jun 2004 20:04:09 -0500
- Subject: Re: 64 bit fortran unformatted on Opteron -- incompatible with32unformatted
Toon Moene wrote:
> Now an interesting question is how we are going to treat this with
> gfortran: On the one hand we can do it right (use one record length
> size on 32-bit and 64-bit systems), but then people on 64-bit systems
> can't read their g77 generated unformatted files - or we could do the
> same as libf2c and be stuck with the above problem.
> On the third hand, I have received requests for 64-bit record lengths
> on either system so that larger-than-2-Gbyte records are possible.
as of right now, the gfortran approach is like this:
each sequential, unformatted record is prefixed with a byte count, of
type off_t. off_t is a 64 bit number on FreeBSD and is a 32 bit number
on Linux (without using the LFS routines).
sequential, unformatted I/O is also broken, the lower level write
routine that spaces back to write this byte count doesn't work; these
facts are only marginally applicable to this discussion:=)
i like the idea that the default is 64 bits for either case, but for
users with an off_t of only 32 bits, they would be restricted to a
record size < 2^32. the run-time could give an error message
"unformatted record size too big" or something.
this of course means you cannot read g77 unformatted files.