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pentium.txt
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1994-12-09
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A quick test to see if the CPU has the FPU problem is to perform the
following calculation (all calculations can be done using the Windows
Calculator or any spreadsheet or math program):
X=4195835*2^n
Y=3145727*2^n
Note: 'n' can be any integer, but must be the same for both
'X' and 'Y'. The 2^n segment of 'X' and 'Y' are optional,
but must in both or neither (in other words you can't leave
the 2^n in the expression for 'X' and not have it in the one
for 'Y').
eqn=(X/Y)*Y-X <---- This is the equation your P5 should calculate.
As anyone who has taken even basic algebra knows, this equation
simplifies to X-X which, of course, equals zero, except on P5 CPU's with
the FPU error.
Other tests:
Divide 5,505,001 by 294,911
buggy answer: 18.66600093
correct answer: 18.66665197
Divide 4,195,835 by 3,145,727
buggy answer: 1.33373907
correct answer: 1.33382045
This error is of little consequence unless you perform math intensive
calculations WHICH UTILIZE THE FPU and have significant digits past 4
decimal places. The odds of hitting the correct sequence of numbers to
generate this error are astronomical otherwise (only 1,378 numbers out
of 64 trillion number combinations have produced the bug thust far,
according to the latest info from Intel...).
Further information can be obtained from Intel's FAXback service at
1-800-525-3019 by requesting document number 9788.
Further info on Internet is available via anonymous ftp at www.isi.edu in
directory /pub/carlton/pentium/FAQ.