Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!hplabs!nsc!taux01!yuval
From: yuval@taux01.UUCP (Gideon Yuval)
Newsgroups: comp.arch
Subject: Re: 88k trick for FP abs/neg
Message-ID: <813@taux01.UUCP>
Date: 7 Jul 88 08:34:06 GMT
References: <10136@tekecs.TEK.COM> <2553@obiwan.mips.COM>
Reply-To: yuval@taux01.UUCP (Gideon Yuval)
Organization: National Semiconductor (Israel) Ltd.
Lines: 16

> Oughtn't the operand be first tested for "IEEE-ness"?  Specifically,
> what if the operand of  neg  is a Signaling NaN?  Oughtn't this cause
> an invalid operation exception?

The "Recommended Functions & Predicates" section of the standard has:

"-x is x copied with its sign reversed, not 0-x; the distinction is germane
when x is +-0 or NaN."

From this, the obvious conclusion is that -NaN is that same NaN with its
sign reversed.

Same goes for abs(x); "abs(x)=copysign(x,1.0), even if x is a NaN".
-- 
Gideon Yuval, yuval@taux01.nsc.com, +972-2-690992 (home) ,-52-522255(work)
 Paper-mail: National Semiconductor, 6 Maskit St., Herzliyah, Israel
             (alternative E-mail address: decwrl!nsc!taux01!yuval@uunet.uu.net)