Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!ncar!tank!uxc!uxc.cso.uiuc.edu!uxg.cso.uiuc.edu!uxe.cso.uiuc.edu!hirchert
From: hirchert@uxe.cso.uiuc.edu
Newsgroups: comp.lang.fortran
Subject: Re: Fortran versus C for numerical anal
Message-ID: <50500074@uxe.cso.uiuc.edu>
Date: 8 Sep 88 20:39:00 GMT
References: <893@amelia.nas.nasa.gov>
Lines: 25
Nf-ID: #R:amelia.nas.nasa.gov:893:uxe.cso.uiuc.edu:50500074:000:1246
Nf-From: uxe.cso.uiuc.edu!hirchert    Sep  8 15:39:00 1988


Dominick Samperi(samperi@djs.UUCP) asks:
>I don't have a copy of the official FORTRAN standard handy, but there appears
>to be an inconsistency in the specifications. Specifically, most references on
>FORTRAN state that the primitive operators associate left to right, except
>for **, which associates right to left. This would imply that A+B+C will
>be evaluated as (A+B)+C.

>On the other hand, I have verified that the FORTRAN definition explicitly 
>allows any FORTRAN implementation to rearrange the order of evaluation of 
>an expression for optimization in any manner, provided that operator 
>precedence rules are obeyed, and parentheses are respected. Does this not 
>contradict the left-to-right/right-to-left rules mentioned above?

Left to right precedence means that A-B+C is interpreted mathematically as
(A-B)+C and not A-(B+C).  Freedom of evaluation order (in the absence of
explicit parentheses) means that mathematical (A-B)+C could be evaluated as
(A+C)-B or even A-(B-C).

>Dominick Samperi
>    samperi@acf8.nyu.edu             uunet!hombre!samperi
>    cmcl2!acf8!samperi               rutgers!acf8.nyu.edu!samperi
>      (^ ell)

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