Conference turris::fortran

    Why use implied DO loops?  Why not just set the recl = array size and
    read one record?
    
    Jim Fohlin
    

You can do that too, though I'm not 100% sure the RTL can handle reading a
3GB array in one swell foop.

				Steve

   Won't using the Fortran RTL imply two copies: one from the Unix IO
   subsystem to the RTL internal buffer, and then from the RTL buffer to
   to the target array?

   Sounds like mmap() would be your best bet, if it were allowed.

   -- John Faricelli

    Could someone confirm that two copies are required?  If they are, that
    could help explain the comments I have heard about slow Fortran I/O.           
    
    mmap() is a good idea.  I have used it for other benchmarks.  But the           
    current RFP requires that I only use Fortran and COTS/GOTS/PD
    libraries.  So unless the mmap() Fortran binding is generally
    available, I can't use it.  Nor can I use my open/close/read/write
    Fortran bindings.
    
    How do I contribute code that would appear as an unsupported subset as
    part of the Fortran kit?  That would solve the problem for this RFP
    and maybe help other people.
    
    Jim Fohlin
    

   You can get the underlying file descriptor that corresponds
   to a  Fortran IO unit number via getfd(3f). That should avoid
   needing a jacket to open(2)/close(2).

   You'd just need a jacket to read(2)/write(2). At one point,
   there was/is an IEEE standard for interfaces to POSIX from Fortran.
   If they had interfaces to read(2)/write(2), then you might want
   to use their calling semantics.

   -- John Faricelli

    Could you please provide more info on the IEEE/POSIX Fortran bindings?
    Does Digital have an implementation?  Is it publically available?
    
    Jim Fohlin
    

    We don't have an implementation.  Almost noone uses them.
    
    				Steve

   The relevant Posix standard for f77 is P1003.9, dated 1992.
   According to a Digital internal chart, the f90 standard was withdrawn.

   According to an old draft, the bindings for read(2) and write(2) are:

   PFXREAD(ifildes, buf, nbyte, nread, ierror)

   integer ifildes     ! file descriptor
   character buf(*)    ! character buffer
   integer nbyte       ! bytes to read
   integer nread       ! bytes actually read
   integer ierror      ! error condition, zero if successful

   PFXWRITE(ifildes, buf, nbyte, nwritten, ierror)

   integer ifildes     ! file descriptor
   character buf(*)    ! character buffer
   integer nbyte       ! bytes to write
   integer nwritten    ! bytes actually written
   integer ierror      ! error condition, zero if successful

   You might do an external AltaVista search, some place like NIST
   might have done a PD implementation of this binding...

   Anyway, from what Steve indicates, sounds like not many vendors
   bought into providing this binding.

   -- John Faricelli


   

   Come to think of it, you don't need extra bindings at all to call read(2)
   or write(2). Just use the cdec$ alias avoid the trailing underscores,
   and %val() where needed.

   Here are some examples, would they be "OK" since they only use Fortran
   (albeit, using nonstandard extensions to Fortran, but your bindings
   would be nonstandard as well).

   -- John Faricelli

** f77_write.f
        implicit none
        integer getfd, fd
        integer IARRAY
        parameter (IARRAY=10)
        integer ibuf(IARRAY), i, nbytes, nwritten, write
c
cdec$   alias write,"write"
c
        do i=1,IARRAY
           ibuf(i) = i
        end do
c
        open(unit=10,file='bintest',status='unknown')
        fd = getfd(10)
        nbytes = IARRAY*sizeof(i)
        nwritten = write(%val(fd),ibuf,%val(nbytes))
        close(unit=10)
c
        write(6,*) 'Number of bytes written: ', nwritten
c
        end

** f77_read.f
        implicit none
        integer getfd, fd
        integer IARRAY
        parameter (IARRAY=10)
        integer ibuf(IARRAY), i, nbytes, nread, read
c
cdec$   alias read,"read"
c
        open(unit=10,file='bintest',status='unknown')
        fd = getfd(10)
        nbytes = IARRAY*sizeof(i)
        nread = read(%val(fd),ibuf,%val(nbytes))
        close(unit=10)
c
        write(6,*) 'Number of bytes read: ', nread
c
        do i=1,IARRAY
           write(6,*) ibuf(i)
        end do
c
        end