Article View: comp.lang.fortran
Article #6550Re: True probabilistic rounding [was Re: Precision ...]
From: Iain McClatchie
Date: Thu, 02 Oct 2003 18:10
Date: Thu, 02 Oct 2003 18:10
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Nick> Apparently it [true probabilistic rounding] is starting to be Nick> adopted in graphics. Whoa! The graphics guys at SGI soured on MADDs when they found out that fused multiply-add instructions round differently than two separate operations. It turns out that you have to calculate the exact same screen position twice for a vertex which is part of two different triangles. The bug they found was that the vertex went down two different code paths, and the two paths rounded differently, in this case because one path used multiply and then add, and the other used a fused multiply-add. Graphics guys are really into repeatability. They'll get their performance by chucking precision or accuracy first.
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X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: fd4af,7830916812112af0 X-Google-Attributes: gidfd4af,public X-Google-Thread: 102b75,7830916812112af0 X-Google-Attributes: gid102b75,public X-Google-Thread: 1094ba,7830916812112af0 X-Google-Attributes: gid1094ba,public X-Google-ArrivalTime: 2003-10-02 11:10:43 PST Path: arc1-ca.pugleaf.net!archiver1.google.com!postnews1.google.com!not-for-mail From: iain-3@truecircuits.com (Iain McClatchie) Newsgroups: comp.lang.fortran,comp.arch,bit.listserv.ibm-main Subject: Re: True probabilistic rounding [was Re: Precision ...] Date: 2 Oct 2003 11:10:43 -0700 Organization: http://groups.google.com Lines: 16 Message-ID: <45022fc8.0310021010.4aaf0e5e@posting.google.com> References: <dG4db.598668$uu5.97984@sccrnsc04> <Rh0eb.632709$Ho3.121617@sccrnsc03> <bla4k2$nas$1@pegasus.csx.cam.ac.uk> <FR0eb.637973$uu5.101567@sccrnsc04> <r%0eb.163529$3o3.11771639@bgtnsc05-news.ops.worldnet.att.net> <bY1eb.633341$Ho3.121512@sccrnsc03> <Zs2eb.157980$0v4.11847973@bgtnsc04-news.ops.worldnet.att.net> <blbcjf$lrn$1@pegasus.csx.cam.ac.uk> <QEbeb.377802$2x.116648@rwcrnsc52.ops.asp.att.net> <blbmni$g2$1@pegasus.csx.cam.ac. <ble09h$pn2$1@pegasus.csx.cam.ac.uk> NNTP-Posting-Host: 64.164.5.210 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-Trace: posting.google.com 1065118243 14883 127.0.0.1 (2 Oct 2003 18:10:43 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Thu, 2 Oct 2003 18:10:43 +0000 (UTC)