Newsgroups: comp.lang.fortran
Path: utzoo!utgpu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!alchemy.chem.utoronto.ca!mroussel
From: mroussel@alchemy.chem.utoronto.ca (Marc Roussel)
Subject: Re: Pseudo-FORTRAN -- f2c for the Macintosh
Message-ID: <1991Jun7.144220.16691@alchemy.chem.utoronto.ca>
Organization: Department of Chemistry, University of Toronto
References: <1991Jun1.171914.802@weyrich.UUCP> <1991Jun5.220805.4653@alchemy.chem.utoronto.ca> <1991Jun7.022834.898@weyrich.UUCP>
Distribution: na
Date: Fri, 7 Jun 1991 14:42:20 GMT

In article <1991Jun7.022834.898@weyrich.UUCP> orville@weyrich.UUCP
(Orville R. Weyrich) writes:
>In article <1991Jun5.220805.4653@alchemy.chem.utoronto.ca>
>mroussel@alchemy.chem.utoronto.ca (Marc Roussel) writes:
>>I can see one possible legitimate use of EQUIVALENCE with different data
>>types: to decide on the endianism of your machine (and similarly to decide
>>other quirks of the number system of the computer).
>
>Of course, you beg the question. Why do you need to know the endianism if you
>are writing standard FORTRAN?

     I feel that my point has been missed.  A standard-conforming
Fortran program doesn't need to know about endianism, of course.  On the
other hand, I believed when I wrote the above that it was possible to write a
standard-conforming program whose sole purpose was to determine
endianism.  To what devious uses you put this information is in some
sense irrelevant (and more than likely non-standard).  It has struck me
since however that since the standard doesn't say what to do when one
equivalences across data types, a particularly odd compiler could
transform the "obvious" meaning of EQUIVALENCE into something else
entirely (and still conform to the standard).  (I believe that this
situation is common when equivalencing any numerical type to CHARACTER
because of the peculiar way in which character variables are stored in
some systems.)  I therefore retract my example.  I don't think you can use
equivalence portably to do anything other than save space.

				Marc R. Roussel
                                mroussel@alchemy.chem.utoronto.ca