Newsgroups: comp.arch
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Standard Un*x H/W architecture
Message-ID: <1988Jul22.162623.5353@utzoo.uucp>
Organization: U of Toronto Zoology
References: <980@garth.UUCP> <76700037@p.cs.uiuc.edu> <12005@ames.arc.nasa.gov> <10298@lll-winken.llnl.gov> <12055@ames.arc.nasa.gov>
Date: Fri, 22 Jul 88 16:26:23 GMT

In article <12055@ames.arc.nasa.gov> lamaster@ames.arc.nasa.gov.UUCP (Hugh LaMaster) writes:
>... One of the nice features of the Cray CFT
>Fortran compiler is a compiler switch which generates an extra
>truncation instruction with each assignment.  You can truncate to the
>desired number of bits and see just how sensitive your code is to small
>truncation errors...

Let us not forget that IBM's Stretch machine (the 7030, late 50s) had a bit
which told the floating-point processor whether to round correctly or
randomly.  Same underlying idea:  run your program twice, with the bit set
differently, and see if the answers differ.  Note that this added zero
overhead (apart from running things twice!), since the floating-point
hardware was just as fast/slow either way.
-- 
Anyone who buys Wisconsin cheese is|  Henry Spencer at U of Toronto Zoology
a traitor to mankind.  --Pournelle |uunet!mnetor!utzoo! henry @zoo.toronto.edu