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From: ags@s.cc.purdue.edu (Dave Seaman)
Newsgroups: comp.lang.fortran
Subject: Re: Fortran versus C for numerical analysis
Message-ID: <3534@s.cc.purdue.edu>
Date: 2 Sep 88 00:51:51 GMT
References: <893@amelia.nas.nasa.gov> <3064@lanl.gov> <338@quintus.UUCP>
Reply-To: ags@s.cc.purdue.edu.UUCP (Dave Seaman)
Organization: Purdue University
Lines: 29

In article <338@quintus.UUCP> ok@quintus.UUCP (Richard A. O'Keefe) writes:
>In article <3064@lanl.gov> jlg@lanl.gov (Jim Giles) writes:
>>The fact that C parentheses don't force execution order is sufficient
>>to exclude C from use in some instances.
>
>Fortran's kludge of using () to control evaluation order (which means that
>it has no way of expressing plain grouping *without* forcing evaluation
>order) has been adopted in the draft ANSI C standard, so this should cease
>to be a problem.

On the contrary, Fortran's parentheses control only grouping and have
nothing to do with evaluation order.  Consider the statement

	Y = A(X) + (B(X) + C(X))

where A, B and C are external functions.  There are 3! = 6 possible orders
of evaluation for the three functions.  All six of them are legal in
Fortran.  For example, a perfectly legal code sequence would be the
following:

	1. Evaluate C(X) and place the result in a temporary, t1.
	2. Evaluate A(X) and place the result in a temporary, t2.
	3. Evaluate B(X) and place the result in a temporary, t3.
	4. Add t3 to t2 and place the result in t3.
	5. Add t3 to t1 and store the result in Y.


-- 
Dave Seaman	  					
ags@j.cc.purdue.edu