Path: csiph.com!x330-a1.tempe.blueboxinc.net!feeder1.hal-mli.net!border3.nntp.dca.giganews.com!Xl.tags.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local2.nntp.dca.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Sat, 14 May 2011 15:22:08 -0500 Message-ID: <4DCEE46F.4020907@SPAM.comp-arch.net> Date: Sat, 14 May 2011 13:22:07 -0700 From: "Andy \"Krazy\" Glew" Reply-To: andy@SPAM.comp-arch.net Organization: comp-arch.net User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.2.11) Gecko/20101013 Thunderbird/3.1.5 MIME-Version: 1.0 Newsgroups: comp.arch Subject: Re: Computer arithmetic problems worth exploring References: <4DCCA37C.6090505@SPAM.comp-arch.net> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Lines: 35 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-VHuPIJ0UrZm9EVmG3qrAcRuvGtMlgvjj7ZvztP5kt5gDOLLijuk0qyksj12+buRWqFvR3W/HhILXYL7!Yxt20kDCIQDTPPS4qzppyAmhWEa/R2QuTgldeNF2wwD9ygnUOyGcQj+oQMll X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 X-Original-Bytes: 3089 Xref: x330-a1.tempe.blueboxinc.net comp.arch:1575 On 5/13/2011 1:48 AM, nmm1@cam.ac.uk wrote: > Andy \"Krazy\" Glew wrote: >> >>>> No, actually, it looked like he was asking leading questions that >>>> pointed in the direction of getting rid of silent NaNs. >>> >>> Yes. There, I agree with him - but every language that I know of >>> that has supported IEEE 754 NaNs has got rid of signalling ones, >>> or deprecated them into near uselessness! >>> >>> I can't tell you whether he lost the argument in 1984 or changed >>> his views, but quiet NaN comparison was one of the things that >>> made me splutter when I first read IEEE 754. I then did a test >>> on myself, and took considerable care coding - but I had still >>> got 20% of the tests wrong for correct NaN handling! >> >> I'm not so sure: quiet NaNs or the equivalent are necessary for things >> like spreadsheets, where you still want to put values into cells even if >> they do calculations like 1/-0(=-inf), or 0/0 or other indeterminate values. >> >> There *must* be a not-number value. Just like null in databases. Data >> occasionally is missing. > > No, that's completely wrong. IEEE NaN has totally the wrong semantics > for missing values, and they are primarily error indicators. I am a > statistician by training, and have worked with some of the people > who introduced missing values into modern computing. > > I have a part-written paper that describes something half a dozen > classes of "Not A Number", and the key factor is that they all have > different and usually incompatible semantics. I'd love to see the paper, half written or not. It sounds like the paper on the 7 different flavors of database null.