Newsgroups: comp.arch
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: IEEE floating point
Message-ID: <1991May25.222551.16365@zoo.toronto.edu>
Date: Sat, 25 May 1991 22:25:51 GMT
References: <9105250030.AA08036@ucbvax.Berkeley.EDU>
Organization: U of Toronto Zoology

In article <9105250030.AA08036@ucbvax.Berkeley.EDU> jbs@WATSON.IBM.COM writes:
>...don't believe it addresses the main sources of error.  I also don't
>believe that IEEE FP is well-designed.  Exactly why do you believe nu-
>merical problems using IEEE FP are more likely to be obvious and pre-
>dictable than numerical problems using IBM hex (for example)? ...

A proper response to this would basically be a detailed defence of IEEE FP's
more controversial design decisions.  I have neither the time nor, really,
the expertise to do this.  However, salvation arriveth from an unexpected
direction. :-)  Go read "What Every Computer Scientist Should Know About
Floating-Point Arithmetic", by David Goldberg, in the latest (March) issue
of ACM Computing Surveys; doing so will enlighten you in detail on the
subject.

I will confine myself to observing that IBM hex FP is the only FP format
I know of that made half the FP instructions -- the single-precision ones --
just about useless to most programmers.
-- 
"We're thinking about upgrading from    | Henry Spencer @ U of Toronto Zoology
SunOS 4.1.1 to SunOS 3.5."              |  henry@zoo.toronto.edu  utzoo!henry