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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: should I be interested in ada?
Date: 1999/02/23
Message-ID: <EACHUS.99Feb23182011@spectre.mitre.org>#1/1
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References: <7a72e6$g55$1@probity.mcc.ac.uk> <36C93BB4.1429@ecs.soton.ac.uk>
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 <7ahkn0$kab$1@plug.news.pipex.net> <36CC6AC0.25DBE56D@erols.com>
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 <36D04A5C.7DE1@lanl.gov>
Organization: The Mitre Corp., Bedford, MA.
Newsgroups: comp.lang.ada
Date: 1999-02-23T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <36D04A5C.7DE1@lanl.gov> William Clodius <wclodius@lanl.gov> writes:

  > The 7090 is before my time and I have done very little, if any, IBM
  > mainframe programming, but I have never heard of Fortran -2. I thought
  > that untill the late 70's IBM consistently used Roman numerals for its
  > Fortran compilers, after the first Fortran compiler

   I programmed a 7090 way back when.  By the time I arrived at MIT,
the 7090s there were, I think, upgraded to 7094's.  (If not the
process was completed within a few months.)

 > In the first volume of the History of Programming languages, edited by
 > Wexelblat, Backus goes into detail about the optimizations available for
 > Forran I and II, which actually match most of the optimizations of
 > interest here, i.e., the optimizations predated both Fortran 66 and the
 > 7090. I suspect you are actually thinking of Fortran II for the IBM 709.

 > Most references I have seen state that Fortran IV was primarilly used to
 > program the 7090, and that for a number of years the Fortran IV compiler
 > had little or no optimization.

   Correct, but anyone doing numerical work on the '90 or '94 used
Fortran II, to get the advantage of the ferocious optimization.  Of
course, you had to throughly debug your code, precisely because of the
problems aliasing could cause during optimization.

 > Another Fortran optimization "problem" is the language's assumption that
 > functions have no significant side effects, which users often want to
 > use for random number generators or warning flags of various kinds. In
 > practice the warning flags usually work (although the language does not
 > define their behavior) when the processor decides to execute the
 > function, but random number generators implemented as functions are a
 > notorious source of hard to detect problems with code.

    I remember, I remember... For the IBM 360 series, there were two
Fortran 66 compilers, FORTRAN G and FORTRAN H.  FORTRAN H had three
optimization levels, 0, 1 and 2.  OPT=0 was stated to be equivalent to
FORTRAN G--it wasn't--and OPT=2 was really fierce.  Typical was to
debug code using FORTRAN G, then try to get it to work as well under
OPT=1.  If it was still too slow, you would start compiling things at
OPT=2 and fixing the things that broke.  Since the problems introduced
by OPT=2 were likely to show up somewhere else, it was handy to do it
this way to localize the problem.  (Where in this file do I reference
that common block?  Okay, here it is what are the other parameters?
Ah ha, an EQUIV!  Nope, that's not it...)

    But for large matrices and number theory work, the only way to go.
(PL-I had huge procedure call overhead.  You could design around it,
but then you might as well use FORTRAN.)

--

					Robert I. Eachus

with Standard_Disclaimer;
use  Standard_Disclaimer;
function Message (Text: in Clever_Ideas) return Better_Ideas is...