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From: lyang%scherzo@Sun.COM (Larry Yang)
Newsgroups: comp.arch
Subject: Re: IEEE floating point modes
Message-ID: <22630@sun.uucp>
Date: Thu, 2-Jul-87 19:40:16 EDT
Article-I.D.: sun.22630
Posted: Thu Jul  2 19:40:16 1987
Date-Received: Sat, 4-Jul-87 08:52:23 EDT
References: <93900007@hcx1>
Sender: news@sun.uucp
Reply-To: lyang@sun.UUCP (Larry Yang)
Organization: Sun Microsystems, Mountain View
Lines: 26

In article <93900007@hcx1> daver@hcx1.SSD.HARRIS.COM writes:
>IEEE floating point arithmetic users:
>
>Of the 4 rounding modes -- nearest, zero, positive infinity, and negative
>infinity -- which one(s) are you most likely to use?  

I am not a real user of floating point arithmetic, but I understand a little
bit about the theory behind the use of the rounding modes.  The round to 
nearest is pretty straight-forward; it's the most obvious rounding mode.
The rounding to +inf and -inf are especially useful in what is known as
'interval arithmetic'.  Since floating point arithmetic has the potential
of inaccuracies due to rounding, what a programmer may do is to perform 
a computation using 'round to +inf', then repeat the computation using
'round to -inf'.  Then they are certain that the 'true' result lies somewhere
between these two bounds; they know the 'interval' in which the solution
lies.

I am not sure about the use of round to zero; I will need to check my notes.

================================================================================


--Larry Yang [lyang@sun.com,{backbone}!sun!lyang]|   A REAL _|> /\ |
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