Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!elroy.jpl.nasa.gov!decwrl!mcnc!duke!sam.cs.olemiss.edu!tacky.cs.olemiss.edu!randy
From: randy@tacky.cs.olemiss.edu (Randy Zagar)
Newsgroups: comp.lang.fortran
Subject: Dumb behaviour in Sun Fortran v1.3.1
Keywords: efficiency complex expressions
Message-ID: <1991Feb16.011005.4289@cs.olemiss.edu>
Date: 16 Feb 91 01:10:05 GMT
Sender: news@cs.olemiss.edu
Reply-To: randy@tacky.cs.olemiss.edu (Randy Zagar)
Organization: University of Mississippi, Dept. of Computer Science
Lines: 25

Sun's F77 v1.3.1 evaluates expressions involving complex numbers inefficiently.
The offending expressions are of the type

    (complex expression) / (real expression)

which are converted to

    (complex expression) / (complex expression)

and then evaluated by complex division.  The expression should be evaluated as

  (complex expression) * (1.0 / real expression)

which only involves a real division and a real multiply.  

Please forgive me if I'm repeating well-known information, but I just achieved 
a 500% increase in application performance by forcing expressions to be evaluated
as I just described.

Randy Zagar                                         (randy@sparc.ncpa.olemiss.edu)
Nat'l Center for Physical Acoustics
The University of Mississippi
Colisium Drive
University, MS 38677
(601)-232-5614