Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!brutus.cs.uiuc.edu!uakari.primate.wisc.edu!uwm.edu!psuvax1!rutgers!deimos!ux1.cso.uiuc.edu!ux1.cso.uiuc.edu!hirchert
From: hirchert@ux1.cso.uiuc.edu
Newsgroups: comp.lang.misc
Subject: Re: NOT Educating FORTRAN programme
Message-ID: <7300006@ux1.cso.uiuc.edu>
Date: 24 Jan 90 21:03:00 GMT
References: <4561@scolex.sco.COM>
Lines: 36
Nf-ID: #R:scolex.sco.COM:4561:ux1.cso.uiuc.edu:7300006:000:1583
Nf-From: ux1.cso.uiuc.edu!hirchert    Jan 24 15:03:00 1990


Sean Eric Fagan (seanf@sco.COM) writes
>In article <14203@lambda.UUCP> jlg@lambda.UUCP (Jim Giles) writes:
>>This is not true.  There is _NO_ case that I'm aware of that parenthesis
>>are _REQUIRED_ in Fortran (ADA, Pascal, etc.) when they are not also
>>_REQUIRED_ in C - and with the _SAME_ consequences with respect to
>>optimization.  It is with _OPTIONAL_ parenthesis that the languages
>>differ.  In C, the compiler ignores them, in all the other languages
>>the compiler must evaluate in parenthesis order.  So, the trade-off you
>>mention is under direct user control in all languages but C.
>
>1.  Given
>	a + b + c - e - f;
>
>I'm happy to let the compiler rearrange things as much as possible to
>generate fast code.  In FORTRAN, by your own admission, you can't do that.

I don't see him admitting this.  In the absence of parentheses, a Fortran
processor is free to choose any mathematically equivalent evaluation order
(even though this might produce different results in the machine arithmetic).
>
>2.  Given
>
>	((((a + b) + c ) -e ) - f);
>
>The compiler is free to rewrite this, *IFF* the result would be the same!
>If you're using shorts, and overflows are ignored, then, probably, it can do
>what it wants to.  If, however, the result is *not* the same, then the
>compiler cannot do this, and, if it does, it's a bug.

Although the Fortran standard is less explicit about this, Fortran processors
are also allowed transformations that don't change the machine results.


Kurt W. Hirchert     hirchert@ncsa.uiuc.edu
National Center for Supercomputing Applications