Subject: DEFECTIVE PENTIUM FPU'S

From: <[email-masked]>
Date: Mon, 21 Nov 1994 15:51:39 -0500

NETTERS: BEWARE OF FPU ERROR IN INTEL 60 AND 90 MHZ PENTIUM CHIPS:

THE FOLLOWING EXPRESSION GIVES A GRIEVOUSLY INCORRECT ANSWER:

Z=X-(X/Y)*Y = 256,  FOR X=4195835 AND Y=3145727.

OBVIOUSLY THE CORRECT ANSWER IS EXACTLY 0, WITHIN ROUND-OFF ERROR.

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

INTEL HAS JUST TOLD ME ON THE PHONE THEY DO NOT CONSIDER THIS A PROBLEM. THEY

SAY THEY HAVE KNOWN ABOUT IT SINCE LAST JUNE.

REGARDS

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John M. McKelvey			email: [email-masked]
Computational Science Laboratory	phone: (716) 477-3335
2nd Floor, Bldg 83, RL
Eastman Kodak Company			
Rochester, NY 14650-2216

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