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Article #12237Re: Error magnitude in i860 fp divide.
From: Alan Christiansen
Date: Sun, 23 Jun 1991 18:36
Date: Sun, 23 Jun 1991 18:36
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1483 bytes
jeff@oakhill.sps.mot.com (Jeff Enderwick) writes: > I'm looking at an old i860 manual, sections 9.2 and 9.3. It appears > that they propose fp division via reciprocal approximation and > multiplication. The manual states that "Worst case error is about > two least-significant bits", for both SP and DP. I've tried doing > some error analysis, and I can't figure out how they came up with > a maximum error figure that small. > Does anyone know how to show this result, or does anyone know the > number for the i860 applications group ? I have not seen the i860 manual you are referring too. I have however seen Motorollas dsp96002 manual and they perform division in a similar way. Using an initial approximation of 1/x then progressive improvement of this accuracy. eventually y/x is found by multiplying an accurate version of 1/x times y. If this is what you are referring too I can explain how the improved accuracy occurs. Alan > Jeff Enderwick > jeff@otis.sps.mot.com
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!caen!spool.mu.edu!munnari.oz.au!bruce!monu0.cc.monash.edu.au!monu6!minyos.xx.rmit.oz.au!stan!saturn!alan From: alan@saturn.cs.swin.OZ.AU (Alan Christiansen) Newsgroups: comp.arch Subject: Re: Error magnitude in i860 fp divide. Message-ID: <1761@stan.xx.swin.oz.au> Date: 23 Jun 91 18:36:41 GMT References: <1991Jun21.203429.20415@oakhill.sps.mot.com> Sender: news@stan.xx.swin.oz.au Lines: 24