Pentium is unreliable for floating-point calculations

John Barton jjb at watson.ibm.com
Wed Nov 30 15:17:38 EST 1994


In article <3beqpr$1h9 at lyra.csx.cam.ac.uk>, tjrc1 at mole.bio.cam.ac.uk (Tim Cutts) writes:
|> prm at aber.ac.uk (Pedro Mendes) writes:
|> 
|> >4195835.0 - (4195835.0 / 3145727.0 ) * 3145727.0
|> 
|> >The result should be 0, but the pentiums seem to think it is 256...
|> 
|> Bear in mind you should make sure that the program doing the
|> calculation is using double precision.  It is apparently only double
|> precision that is affected.
|> 
|> Tim.

   Just so I don't miss out in the incredible net traffic on this one...
I wonder what percentage of the world's numerical software is
more accurate than this erroneous chip?  One part in 10**6?

-- 
John.

John J. Barton        jjb at watson.ibm.com            (914)784-6645
H1-C13 IBM Watson Research Center P.O. Box 704 Hawthorne NY 10598




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