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Floating Point Error Intel


iliyapolak Mon, 03/03/2014 - 04:05 Looks like rounding issue.Are those values i.e x and  1.0000000/8.5404000  declared as a double precision? Retrieved 2006-12-19. ^ Alexander Wolfe. "Intel fixes a Pentium FPU glitch". ^ "Intel adopts upon-request replacement policy on Pentium processors with floating point flaw; Will take Q4 charge against earnings". Distribute new product announcements, sure. Hundreds of manufacturers, domestic and international, participated in this campaign, and Intel spent a lot of money promoting the brand. weblink

A: Repentium. Is it necessary to ensure ALL double precision arrays are aligned on windows or linux platforms even if you are not using MKL UNLESS you use fp:precise? Steve Smith of Intel says the Pentium processor's problem is minor. Magazine interviews and ultimately a CNN interview followed. check these guys out

Intel Pentium Chip Flaw Of 1994 Case Study

All rights reserved. It should not have been released on the Internet first. Nicely's original message.) All hell breaks loose on the newsgroup. Mon, 03/03/2014 - 07:55 I think the Fortran standard issue to which Craig refers is that literal floating point constants with no type specification are to be interpreted as default real.

And it dedicates four fulltime employees to read Internet newsgroups and respond immediately to any postings about Intel or its products. First, you must identify these instigators. Intel Applications Support Manager Ken Hendren posts a message on America Online and the Internet, revealing that Intel has no one providing customer support on the Internet. Pentium F00f Bug Denormalized numbers and gradual underflow are supported, but abrupt underflow is the default at all optimization levels except -O0.

An error was made in this script that resulted in a few lookup entries ... How Did Intel Handle The Pentium Microprocessor Flaw The flaw appears in all Pentium chips now on the market, in certain types of division problems involving more than five significant digits, a mathematical term that can include numbers before Intel said the problem came to its attention in June and was corrected then, at the design stage. http://www.willamette.edu/~mjaneba/pentprob.html Nicely at Lynchburg College,[1] Intel attributed the error to missing entries in the lookup table used by the floating-point division circuitry.[2] The severity of the FDIV bug is debated.

Log in to post comments Martyn Corden (... Intel Division You can only expect about 7 decimal digits to agree. My guess is that the crash is due to floating point arithmetic difference between two compliers and the following property options of the project in two different compliers are not aligning BYTE (March 1995).

How Did Intel Handle The Pentium Microprocessor Flaw

For similar reasons, the options -ansi and -fmath-errno may result in calls to math functions that are implemented using x87 rather than Intel IMCI. In addition to its growing role in PC's, the Pentium chip is used in a number of larger computers that harness individual chips to work in tandem, creating supercomputer power. Intel Pentium Chip Flaw Of 1994 Case Study Intel said, "Pentium chips have a flaw, but it doesn't matter." Intel's customers said, "It does too matter." Intel responded "No, it doesn't," and even though Intel meant well, thousands of Thomas Nicely In this article I will try to summarize what the fuss was about, and some of the mathematics involved.

said on Mon, 01/03/2011 - 16:25 with icc 12.0/xe 2011, more optimizations which are removed by /fp:source can be restored for an individual loop by #pragma simd (which may set /fp:fast have a peek at these guys Top andrew_4619 Wed, 03/05/2014 - 05:24 You are at the limits of the precision chosen. There is a real numerical uncertainty in the result of almost all floating-point calculations. Wed, 03/05/2014 - 06:41 Quote:David Mccabe wrote: @John Campbell: thanks, ftn95 produces the same result as yours using single precision throughout - the reason being that there is no addition in Intel Fdi

Internet analysts immediately demonstrate that IBM's claims are exaggerated, but at the same time no one believes Intel. Resistance is futile. But if a directive specifies that a reduction loop is to be threaded using OpenMP, the compiler is not at liberty to change that. http://bigvideogamereviewer.com/floating-point/floating-point-error-c.html If you're reading about Itanium division expression evaluation methods, forget it, those are unique to Itanium.

The problem does not occur on the specific use of the divide instruction to compute the reciprocal of the input operand in single precision. Pentium Fdiv Bug Cost Unlike traditional news media, the Internet has no filtering process. Intel managers decide that the error will not affect many people and do not inform anyone outside the company.

Why worry about it?

Though case1 runs on the new complier and matches the output of case1 from the built via old complier, case2 first diverges and then crashes (NaN) on the new complier. Mon, 03/03/2014 - 04:50 Are you comparing results with implicit promotion to double vs. The setting -fp-model fast=2 sets the -fimf-domain-exclusion switch and enables faster, inlined versions of some math functions for the Intel Xeon Phi Coprocessor, see the section "Precision of Math Functions" below. Pentium Flaw Research Paper Consequently many users may never encounter the division error.

Once you make human contact, however, it's easier to conduct a give-and-take discussion. Intel has used this tactic with repeated success. We dramatically improved our validation methodology to quickly capture and fix errata, and investigated innovative ways to design products that are error-free right from the beginning. Top Tim P. http://bigvideogamereviewer.com/floating-point/floating-point-error-dos.html Remember that anything on the Net can be picked up by traditional media.

The behavior of the -fp-model precise option is the same, though the consequent reduction in performance may be somewhat greater for Intel Xeon Phi coprocessors, because of the larger vector width A: The warning label. The situation degrades to a point past any logical response. Give the person your direct phone number and ask them to please call at his or her earliest convenience so you can clear this up immediately. All research results are posted in public on the Net for the world to criticize and contribute to.

Wednesday, October 19: After testing on several 486 and Pentium-based computers, Dr. I have 2 run cases, case1 and case2. Chart shows an example of the way the imprecise rounding changes the results of a calcuation and the way the deviation from the expected result is calcucated. (Source: Cleve Moler, the The instructions FPTAN and FPATAN are also susceptible.

If you want ia32 mode, implying implicit promotion to double, and no auto-vectorization, with win32 compilation you would set /arch:IA32 but then you could not expect bit-wise agreement with results in Please read Tim Prince's comments, as well. 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 Log in to post comments Add a Comment Top (For technical discussions visit our developer forums.

This topic also comes up with MKL (we have protected all of our double precision arrays passed to MKL to be 16-byte boundary aligned), but that is not practical to do He forwards Dr. The Intel version of Casablanca: "Round off the usual suspects." Q: How many Pentium designers does it take to screw in a light bulb? Nicely's message to important Phar Lap customers, to Intel, and to people at compiler companies, including Microsoft, Borland, Metaware, and Watcom.

Related instructions that are affected by the bug are FDIVP, FDIVR, FDIVRP, FIDIV, FIDIVR, FPREM, and FPREM1. These alignment considerations apply equally to single and double precision variables. said on Thu, 10/08/2009 - 19:27 It might be noted that it is practical to re-enable certain performance features which are removed by -fp:source e.g. -fp:source -Qftz Future CPUs are planned It has determined that even a large feeding frenzy is usually fueled by five or six instigators, or fewer.

A hundred newsgroup postings do not have the impact of one story in the New York Times. The "correct" answer above is in fact only correct for a particular definition of correct and is truncated from (my calculator value of) 0.11709053440119900707226827783242 The compilers/processors would store this result as single precision Links updated April 20, 2011 Prof.