# Intel Floating Point Bug

## Contents |

These are useful **even if** every floating-point variable is only an approximation to some actual value. Cyclically sort lists of mixed element types? Pentium P5 800nm 5V Family Model Stepping Core stepping Clock rate FSB speed S-spec 5 1 3 B1 60 MHz 60MHz Q0352, Q0412, SX753 5 1 3 B1 66 MHz 66MHz Also, long mode doubles the registers for SSE, giving you 16 XMM registers rather than the 8 available in 32-bit mode, which implies that more data is in need of saving. weblink

Similarly if one operand of a division operation is a NaN, the quotient should be a NaN. all 8 tag registers are not marked as "empty"), and a PUSH instruction is executed, a FPU stack-overflow exception will occur. Even though the computed value of s (9.05) is in error by only 2 ulps, the computed value of A is 3.04, an error of 70 ulps. The section Guard Digits discusses guard digits, a means of reducing the error when subtracting two nearby numbers.

## Intel Floating Point Bug

The zero finder does its work by probing the function f at various values. Though rarely encountered by most users (Byte magazine estimated that 1 in 9 billion floating point divides with random parameters would produce inaccurate results),[3] both the flaw and Intel's initial handling Each floating point register holds an 80-bit extended double value (1-bit sign, 15-bit exponent, and 64-bit fractional value), and each register has a matching 2-bit "tag" value in the Tag Register Addition is included in the above theorem since x and y can be positive or negative.

How to handle a senior developer diva who seems unaware that his skills are obsolete? Is it appropriate to tell my coworker my mom passed away? Probably the most interesting use of signed zero occurs in complex arithmetic. Floating Point Rounding Error The expression x2 - y2 is another formula that exhibits catastrophic cancellation.

Code to implement this technique looks like this: // Usable AlmostEqual function bool AlmostEqual2sComplement(float A, float B, int maxUlps) { // Make sure maxUlps is non-negative and small enough that There is a way to rewrite formula (6) so that it will return accurate results even for flat triangles [Kahan 1986]. What does a well diversified self-managed investment portfolio look like? When rounding up, the sequence becomes x0 y = 1.56, x1 = 1.56 .555 = 1.01, x1 y = 1.01 .555 = 1.57, and each successive value of xn increases by

How? Floating Point Arithmetic Examples This caused the Pentium's FPU to incorrectly divide certain floating-point numbers. Suppose that the final statement of f is return(-b+sqrt(d))/(2*a). Privacy policy About Wikipedia Disclaimers Contact Wikipedia Developers Cookie statement Mobile view Numerical Computation Guide Appendix D What Every Computer Scientist Should Know About Floating-Point Arithmetic Note – This appendix is

## Pentium F00f Bug

This idea goes back to the CDC 6600, which had bit patterns for the special quantities INDEFINITE and INFINITY. Nicely noticed some inconsistencies in the calculations on June 13, 1994, shortly after adding a Pentium system to his group of computers, but was unable to eliminate other factors (such as Intel Floating Point Bug A less common situation is that a real number is out of range, that is, its absolute value is larger than × or smaller than 1.0 × . Pentium Microprocessor Flaw Effectively this means that the comparison only works if one or more of the floats is positive.

Not the answer you're looking for? have a peek at these guys Reiser and Knuth [1975] offer the following reason for preferring round to even. If you do a calculation and then compare the results against some expected value it is highly unlikely that you will get exactly the result you intended. It is not possible to directly copy values from a CPU register to an FPU register. Thomas Nicely

Two examples are given to illustrate the utility of guard digits. Retrieved 5 April 2016. ^ Tom R. With or without rounding. check over here In the = 16, p = 1 system, all the numbers between 1 and 15 have the same exponent, and so no shifting is required when adding any of the (

is the same as 2.0 . Intel Pentium Chip Flaw Of 1994 Case Study By displaying only 10 of the 13 digits, the calculator appears to the user as a "black box" that computes exponentials, cosines, etc. Comparing with epsilon – absolute error Since floating point calculations involve a bit of uncertainty we can try to allow for this by seeing if two numbers are ‘close’ to each

## When p is even, it is easy to find a splitting.

For the calculator to compute functions like exp, log and cos to within 10 digits with reasonable efficiency, it needs a few extra digits to work with. FNINIT will reset the user-visible part of the FPU stack. What does ã‹ãŽã®ã‚ã‚‹ãƒ± mean? Floating Point Calculator There are many bad fpus out there, mostly patched in software if they can catch the instruction or exception, that kind of thing.

If the result is one million then an error of 1.0 is great. However, if there were no signed zero, the log function could not distinguish an underflowed negative number from 0, and would therefore have to return -. One risk is that int and float might not be the same size. this content IEEE 854 allows either = 2 or = 10 and unlike 754, does not specify how floating-point numbers are encoded into bits [Cody et al. 1984].

Not the answer you're looking for? http://adtmag.com/articles/2000/03/16/comparing-floats-how-to-determine-if-floating-quantities-are-close-enough-once-a-tolerance-has-been.aspx share|improve this answer answered Apr 28 '10 at 21:22 ajs410 1,2741313 add a comment| up vote 0 down vote I worked on a team that created an FPU (hardware design) check the tables in the following link if you dont know how to format with printf. ( you can use the formating for rounding and displaying the numbers correctly ) printf Benign cancellation occurs when subtracting exactly known quantities.

Thus there is not a unique NaN, but rather a whole family of NaNs.