Path: utzoo!attcan!uunet!husc6!rutgers!cmcl2!lanl!beta!dd
From: dd@beta.lanl.gov (Dan Davison)
Newsgroups: comp.lang.fortran
Subject: CFT/CFT77 gotcha
Keywords: truncation 47 vs. 48 bits
Message-ID: <23252@beta.lanl.gov>
Date: 21 Jan 89 05:54:28 GMT
Organization: Los Alamos National Laboratory
Lines: 20


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.

Apparently CFT did the equivalent of a NINT() after a force-to-
integer; CFT77 doesn't.  One consultant here said it had to do
with the loss of precision in the last bit, which makes sense.
Another consultant said the moral was don't used mixed mode
arithmetic if you want accurate results.

At least I didn't write the code!  Now, is this a bug or a feature?

A look through the back of the CFT77 manual (Appendix B) indicates
that I'm going to become very familiar with NINT() and IDNINT()...