Re: Fast I/O

Article View: comp.lang.fortran

Article #4451

#4451

From: Steve Lionel
Date: Thu, 21 Jan 1993 14:15

32 lines
1630 bytes

In article <1993Jan21.081105.4047@molene.ifremer.fr>, 
molagnon@ditigo.ifremer.fr (Michel Olagnon) writes:
|>
|>Many Fortran compilers are not efficient on I/O with implied DO loops.
|>Replacing 
|>      write (lu) (a (j), j=1,n)
|>with
|>      call fstwrt (lu, a, n)
|>         .
|>         .
|>      subroutine fstwrt (lu, a, n)
|>      double precision a (n)
|>      write (lu) a
|>      return
|>usually gives dramatic improvement.
|>
|>I have a follow-up question : why don't compilers execute this optimization ?
|>

Digital's VAX FORTRAN does.  It also optimizes some more complex implied
DO-loops, including those with non-unity strides and with expressions in
the array subscript, as long as it can tell that the stride is constant.
If the stride is 1, the I/O operation occurs directly from the array memory
rather than being copied to a buffer.
--

Steve Lionel                    lionel@quark.enet.dec.com
SDT Languages Group
Digital Equipment Corporation
110 Spit Brook Road
Nashua, NH 03062

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From: lionel@quark.enet.dec.com (Steve Lionel)
Subject: Re: Fast I/O
Message-ID: <1993Jan21.141503.22670@dbased.nuo.dec.com>
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Reply-To: lionel@quark.enet.dec.com (Steve Lionel)
Organization: Digital Equipment Corporation, Nashua NH
References: <1jhqkhINNno3@bigboote.WPI.EDU> <1993Jan21.081105.4047@molene.ifremer.fr>
Date: Thu, 21 Jan 1993 14:15:03 GMT

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