Finding Wrong Factors
 

One of my machines seems to have been reporting invalid factors for several exponents for about the past week.

For example, trying to Factor=999787769,68,69 it found 311742316172014440111. I tried on another machine and found 311742316172019240401, which PrimeNet accepts as a correct factor.

I have a list of several other exponents that the machine has reported invalid factors for and so far, testing them on another machine, Prime95 is finding factors for all of them (but these factors are not the same as found by the problem machine).

Problem machine is Core2Quad running mprime 25.11 64-bit on Ubuntu 10.04. I think the problem started last Friday either during or after upgrading Ubuntu.

Has anyone else seen anything like this?



Addition: There is a pattern with the invalid factors. In the last seven digits of each invalid factor, the last three digits are always the same and the first three are always the same.

Samples
 

[FONT=Courier New][B]Exponent, B1,B2,ValidResult, InvalidResult[/B]
[/FONT][FONT=Courier New] 999787909,68,69,364402019246111335271,364402019246113335111[/FONT]
[FONT=Courier New]999716329,67,68,283325467725791515751,283325467725791115111
999716857,66,68,145165997612689815431,145165997612681115111
999717847,66,68,92591053177289526719,92591053177282226999
999251047,64,66,29719878604475321761,29719878604472221111
999251849,65,66,65825810769585187513,65825810769588887333
999252487,64,66,24647063161392847729,24647063161394447999
999253403,65,66,44269948430491857209,44269948430495557999
999254323,65,66,39011818845866218711,39011818845861118111
999255583,64,66,18915642833869934351,18915642833863334111
999257041,64,66,25428544219525899913,25428544219529999333
999257953,64,66,32968409107927176953,32968409107927776333
999258649,65,66,58752059026124461463,58752059026126661333
999260393,64,66,23349847179324681097,23349847179328881777
999260429,64,66,23661497880754771511,23661497880757771111
999261217,64,66,36307571671942157641,36307571671945557111
999261707,65,66,46750191615520862393,46750191615526662333
999262037,64,66,23895719937861499367,23895719937869999777
999262283,65,66,42606646060109502097,42606646060100002777
999262631,64,66,32822562818452800359,32822562818450000999
999263149,64,66,22448473454513813969,22448473454511113999
999266251,65,66,66870317015175339073,66870317015173339333
999266423,64,66,31741872264610755119,31741872264615555999
999266777,65,66,45512757982714266191,45512757982716666111
999266977,64,66,27550584757295047969,27550584757294447999
999270637,65,66,53058372939852700001,53058372939850000111
999271159,65,66,66535988907000045007,66535988907004445777
999272783,64,66,23521656269340045679,23521656269344445999
999274337,65,66,37498518416066705369,37498518416060005999
999276263,64,66,25049443710474931151,25049443710473331111
999279923,65,66,49038501027976076311,49038501027977776111
999280829,65,66,72060146189774967767,72060146189776667777
999284873,64,66,33967769329248966287,33967769329246666777
999285181,64,66,22741625647381979383,22741625647387779333
999286517,64,66,18525141525344525713,18525141525342225333
999287203,64,66,24768613367294831663,24768613367293331333
999288803,64,66,32062439854201483583,32062439854208883333
999290317,64,66,23895568803495442943,23895568803494442333
999292009,64,66,30309933338329653319,30309933338325553999
999293377,65,66,43457038550906883017,43457038550908883777
999293929,65,66,39273076378801673809,39273076378807773999
999296783,64,66,22492927843861912673,22492927843861112333
999297241,64,66,19582088103535274071,19582088103537774111
999297731,64,66,28701964912569773519,28701964912567773999
999299957,64,66,33163716538780200311,33163716538780000111
[/FONT]

Intriguing! The second and third digits (from the right) are replaced by the first digit, and the sixth and seventh digits are replaced by the fifth digit. I don't see how this could be caused by a hardware error. At least your machine is not missing factors, even though the tests have to be rerun on another machine.

Intriguing, indeed!

My top 2 cents is on either a bug or a random byte in the hex-to-decimal conversion function. I'd compare md5-sums of the prime95 executables to see if they match or not.

Here are the checksums from two versions of mprime that I have tried. Both versions find bad factors.


mprime from mprime259-linux64.tar.gz[INDENT] md5sum d268e83943cd1c32fa53854766eae2ba
sha1sum b3e1b636f02c5f26a8c19e75e59b23c605ae2e69
[/INDENT]mprime from mprime2511-linux64.tar.gz[INDENT] md5sum 5a0070a4f93b4f39cf6b9fb0020f3030
sha1sum 72ee20dee3004c6dae792497f801f37afb981710[/INDENT]

[quote=lindee;216524]Here are the checksums from two versions of mprime that I have tried. Both versions find bad factors.


mprime from mprime259-linux64.tar.gz[INDENT] md5sum d268e83943cd1c32fa53854766eae2ba
sha1sum b3e1b636f02c5f26a8c19e75e59b23c605ae2e69
[/INDENT]mprime from mprime2511-linux64.tar.gz[INDENT] md5sum 5a0070a4f93b4f39cf6b9fb0020f3030
sha1sum 72ee20dee3004c6dae792497f801f37afb981710[/INDENT][/quote]

I actually meant comparing the executable in the .tar with the one installed, but since you've run both versions and both display the factors incorrectly, that cannot be it!

What about a bug in a shared library? I have no idea which libraries mprime is dynamically linked with, but if I'm right, then reinstalling/upgrading e.g. glibc should fix the problem.

There were some updates available, so I installed and rebooted. Still no luck.

Here's my current libc information (selected output from 'dpkg -l | grep libc'):

ii libc-bin 2.11.1-0ubuntu7.1 Embedded GNU C Library: Binaries
ii libc-dev-bin 2.11.1-0ubuntu7.1 Embedded GNU C Library: Development binaries
ii libc6 2.11.1-0ubuntu7.1 Embedded GNU C Library: Shared libraries
ii libc6-dev 2.11.1-0ubuntu7.1 Embedded GNU C Library: Development Librarie

What happens if you boot using a 64-bit live-CD from a different distro, run mprime (should have no errors), chroot, and run mprime again?

[QUOTE=__HRB__;216534]What happens if you boot using a 64-bit live-CD from a different distro, run mprime (should have no errors), chroot, and run mprime again?[/QUOTE]

Someone else should try to rerun those factors. could be something about the large exponents, maybe only on linux 64

[QUOTE=lfm;216595]Someone else should try to rerun those factors. could be something about the large exponents, maybe only on linux 64[/QUOTE]
64 bit mprime (both v25.11 build 2 and v25.9 build 4) found the correct factors in Ubuntu 9.04 64-bit on a Core2Quad Q9400.

[quote=lindee;216490]Problem machine is Core2Quad running mprime 25.11 64-bit on Ubuntu 10.04. I think the problem started last Friday either during or after upgrading Ubuntu.[/quote]

[quote=markr;216612]64 bit mprime (both v25.11 build 2 and v25.9 build 4) found the correct factors in Ubuntu 9.04 64-bit on a Core2Quad Q9400.[/quote]

I think that settles that we're not following in Thomas R. Nicely's footsteps. My bottom dollar is on a bug in a shared library in the (or your) Ubuntu installation/configuration.