Subject: RE: Defective PENTIUM FPU's

From: [email-masked] (Tom Pierce)
Date: Mon, 28 Nov 1994 21:02:16 -0500

Previously David J. Heisterberg ([email-masked])  wrote (in response to John
McKelvey):

>>NOW WHAT? COMPUTE STATISTICAL PROBABILITIES OF ERRORS IN COMPUTED RESULTS?

>Tim Coe at Vitesse Semiconductor has done just that.  He's posted a
>very detailed description of the problem in the comp.arch.arithmetic
>news group.  For the likelyhood of running into this bug he says
>  that needs clearing is that this is an extended precision problem.  This
>  bug hits between 50 and 2000 single precision dividend divisor pairs (out
>  of a total of 64 trillion.)
>His analysis shows that the probability of getting a relative error
>greater than 1e-5 is 3e-12, of less than 1e-5, 6e-12.  As to when this
>error occurs
>  Examination of the above divide failures reveals that both the dividend
>  and divisor are integers minus small deltas.  Also notable is the induced
>  error is roughly delta^(2/3).  The integers in the divisors are actually

Hmmm - integer minus small delta's ala x-y=4195835-3145727=1050108,
a large delta, and the error is 256 -> delta^2/3 =4096 not 1,050,108.

I am unhappy with the processor, and now will not use it for calculations...
Maybe I should send it back... Where is that warranty card... 

--
Sincerely,

Tom Pierce Ph.D.