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Floating Point Error Intel


Remember that anything on the Net can be picked up by traditional media. As a result, the value returned by a flawed Pentium processor is incorrect at or beyond four digits:[9] 4 , 195 , 835 3 , 145 , 727 = 1.333 739068902037589 Intel offered to replace processors to users who could prove that they were affected. Log in to post comments Tim P. his comment is here

Indeed, the company said it was continuing to send computer makers Pentium chips built before the problem was detected. program fptest real x,rx x=8.5404000 rx=1.0/x if(abs(x*rx - 1.0).lt.epsilon(x))then   write(*,*)'Correct' else   write(*,*)'Error' endif end program fptest Top Craig Dedo Mon, 03/03/2014 - 06:52 Quote:mecej4 wrote: Quote: David Mccabe wrote:I This may be old, "dusty deck" source code, from the days of Fortran 77 or before.  The Fortran 77 standard allowed a Fortran compiler to "promote" a constant from SP to Then results will differ, and if you have a requirement to match a "certified" set of results then you will not be able to migrate to the newer technology. https://en.wikipedia.org/wiki/Pentium_FDIV_bug

Intel Pentium Chip Flaw Of 1994 Case Study

In this article I will try to summarize what the fuss was about, and some of the mathematics involved. And it dedicates four fulltime employees to read Internet newsgroups and respond immediately to any postings about Intel or its products. This technique, known as parallel processing, is used for weather forecasting, the aerodynamic simulation used in automotive and airplane design and in molecular engineering.

Retrieved 2009-11-10. ^ "Pentium FDIV bug - a Picture". All rights reserved. It has determined that even a large feeding frenzy is usually fueled by five or six instigators, or fewer. Pentium F00f Bug Hundreds of manufacturers, domestic and international, participated in this campaign, and Intel spent a lot of money promoting the brand.

Intel still claims there is no problem. How Did Intel Handle The Pentium Microprocessor Flaw But since, as noted above, -fp-model strict suppresses Intel IMCI in favor of legacy x87 floating-point instructions, this additional behavior is moot. However, FMA generation is an optimization, and since the compiler may sometimes make different FMA optimization decisions for different platforms, you may still be able to reduce differences further with -no-fma. http://www.willamette.edu/~mjaneba/pentprob.html Compiler options give the user control over the tradeoffs between optimizations for performance, accuracy, reproducibility of results and strict conformance with these standards.

If someone posts exaggerated or angry newsgroup messages or sends flaming email about your business, you can employ the procedures Intel now uses. Intel Division D5) Chart: "Close, but Not Close Enough" The owners of computers that use Intel's Pentium microprocessors have found that the chips sometimes do not perform division calculations accurately enough. The uproar started and grew on the Internet. The error can occur in any of the three operating precisions, namely single, double, or extended, for the divide instruction.

How Did Intel Handle The Pentium Microprocessor Flaw

For site or software product issues contact support.) Please sign in to add a comment. This makes them much faster for intense numerical calculations, more complex, and more expensive. Intel Pentium Chip Flaw Of 1994 Case Study Who are the people who feed the flow? Thomas Nicely figs, while the flawed Pentium's floating-point unit computed 1.33374 to 6 sig figs, a relative error of 0.006%.

The most famous example and the worst well-known case is 4195835/3145727, discovered by Tim Coe of Vitesse Semiconductors. this content Retrieved 2010-11-03. ^ "Pentnt". Often convergence code which were formerly tweaked to the limits of x87 will not work when using SIMD instructions. Room for Debate asks whether shorefront homeowners should have to open their land to all comers. Intel Fdi

When the alignment changes, then the number of iterations in the prolog and epilog may change. The 39 S-specs of those processors are not listed in the Intel processor specification finder web page. After the Pentium flaw was made public, Intel began telling users that it had discovered and corrected the flaw in June, and last week it quietly began offering replacement chips to weblink Did you run it with ftn77, as ftn95 is treating it as 8.54040e0 ?

References: Statistical Analysis of Floating Point Flaw in the Pentium (TM) Processor (1994), Sharangpani and Barton, Intel Corporation, Nov. 30,1994. Pentium Fdiv Bug Cost The correct values all would round to 1.3338, but the returned values are 1.3337, an error in the fifth significant digit. Use /fp:precise /fp:source (Windows*) or -fp-model precise -fp-model source (Linux* or OS X*) to improve the consistency and reproducibility of floating-point results while limiting the impact on performance.

Thanks Build 20101201 Package ID: w_cprof_p_11.1.072   AttachmentSize Download test_kind_1.rar95.32 KB RSS Top 19 posts / 0 new Last post For more complete information about compiler optimizations, see our Optimization Notice.

Nicely sends an email message to a few people, announcing his discovery of a "bug" in Pentium processors. (Click to read Dr. We set our own quality levels and specifications, and shipped when we decided a product met our own criteria. SAVE NOW Subscribe Log In Register Now Help Home Page Today's Paper Video Most Popular Edition: U.S. / Global Search All NYTimes.com Business Day World U.S. Pentium Flaw Research Paper The 486DX and Pentium chips have these instructions built into the chip, in their FPUs.

A discussion with someone from Intel once convinced a total flamer to ameliorate his previous newsgroup postings. Previous Intel CPUs did all their arithmetic using integers; programs that used floating-point numbers (non-integers like 2.5 or 3.14) needed to tell the chip how (for example) to divide them using 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 check over here This throws off the calculation and results in a less precise number than the correct answer(Byte Magazine, March 1995).

The differences between the "correct" and "incorrect" answers is too small to represent with default REAL precision. Single (32-bit) and double (64-bit) precision are supported in hardware; quadruple (128-bit) precision is supported through software. p.9. The problem for Intel is that all Pentiums manufactured until sometime this fall had errors in the on-chip FPU instructions for division.

Following an eight-year stint at ITProPortal.com where he discovered the joys of global techfests, developing an uncanny attraction for anything silicon, Désiré now heads up TechRadar Pro. Before using /fp:precise I was getting two different results when passing an external subroutine to an external bisection routine and when using the same bisection routine but copied as a local At this point, an offer by Intel to replace any flawed Pentium chips would have smoothed the waters.