Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-lcc!ames!hc!lanl!beta!dd
From: dd@beta.lanl.gov (Dan Davison)
Newsgroups: comp.lang.fortran
Subject: Re: CFT/CFT77 gotcha
Summary: no warning
Message-ID: <23281@beta.lanl.gov>
Date: 25 Jan 89 03:25:15 GMT
References: <23252@beta.lanl.gov> <50500099@uxe.cso.uiuc.edu>
Organization: Los Alamos National Laboratory
Lines: 35

In article <50500099@uxe.cso.uiuc.edu>, hirchert@uxe.cso.uiuc.edu writes:
> dd@beta.lanl.gov writes
> >I came across an interesting non-bug in CFT77 today.  A program
> >fragment:
> >	a = 6.0
> >	b = 3.0
> >	i = a / b
> >
> >gave the result "2" in CFT on a X/MP-48 and "1" in CFT77 on the
> >same machine.
> [...]  In developing CFT77, CRAY recognized that this
> extra multiply slowed down all divides in this kind of situation, not just
> those that were expected to be exact and that it could be confusing to get
> different results depending on whether or not you assigned the intermediate
> REAL quotient to a variable, so they chose not to do "strong rounding" in this
> case and instead issue a warning message.  (Did you ignore this warning message,
> dd?)


There was no warning issued!  The compiler didn't blink on it.

And thanks very much for an excellent discussion of what was going on.




[inews fodder]



dan davison/theoretical biology/t-10 ms k710/los alamos national laboratory
los alamos, nm 875545/dd@lanl.gov (arpa)/dd@lanl.uucp(new)/..cmcl2!lanl!dd
"Freedom is a heavy load, a great and strange burden for the spirit to
undertake.  It is not easy.  It is not a gift given, but a choice made,
and the choice may be a hard one." ...Le Guin, _The Farthest Shore_