mersenneforum.org Output bug in mmff
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2012-09-17, 23:23   #1
ATH
Einyen

Dec 2003
Denmark

325310 Posts
Output bug in mmff

Ops I thought this was a typo on http://www.prothsearch.net/fermat.html but instead it seems to be a bug in mmff:

Quote:
 F43 has a factor: 3916660235220715932328394753 [TF:91:92:mmff 0.23 mfaktc_barrett96_F32_63gs] found 1 factor for k*2^45+1 in k range: 111318G to 111319G (92-bit factors) [mmff 0.23 mfaktc_barrett96_F32_63gs] F85 has a factor: 246947940268608417020015902258307792897 [TF:127:128:mmff 0.23 mfaktc_barrett128_F64_95gs] found 1 factor for k*2^87+1 in k range: 1595G to 1596G (128-bit factors) [mmff 0.23 mfaktc_barrett128_F64_95gs]
These 2 factors 111318179143061*245+1 and 1595863660157*287+1 are actually factors of F42 and F83 like the webpage reports not F43 and F85 as mmff reports, I checked this in c++ with GMP library as well.

Can someone correct the title of the thread?

Last fiddled with by ATH on 2012-09-17 at 23:47

2012-09-17, 23:52   #2
ATH
Einyen

Dec 2003
Denmark

62658 Posts

Found a third one:

Quote:
 F118 has a factor: 4563438810603420826872624280490561141381005313 [TF:151:152:mmff 0.23 mfaktc_barrett152_F96_127gs] found 1 factor for k*2^120+1 in k range: 3G to 4G (152-bit factors) [mmff 0.23 mfaktc_barrett152_F96_127gs]
This factor 3433149787*2120+1 is a factor of F116, not F118.

2012-09-18, 01:43   #3
R. Gerbicz

"Robert Gerbicz"
Oct 2005
Hungary

5FB16 Posts

Quote:
 Originally Posted by ATH Ops I thought this was a typo on http://www.prothsearch.net/fermat.html but instead it seems to be a bug in mmff: These 2 factors 111318179143061*245+1 and 1595863660157*287+1 are actually factors of F42 and F83 like the webpage reports not F43 and F85 as mmff reports, I checked this in c++ with GMP library as well. Can someone correct the title of the thread?
Yes, it is a serious bug. Have you checked that this code finds all known Fermat (prime) divisors (and the code doesn't contain them in a big table)

Last fiddled with by R. Gerbicz on 2012-09-18 at 01:46

2012-09-18, 02:11   #4
ATH
Einyen

Dec 2003
Denmark

3,253 Posts

Quote:
 Originally Posted by R. Gerbicz Yes, it is a serious bug. Have you checked that this code finds all known Fermat (prime) divisors (and the code doesn't contain them in a big table)
I checked all larger factors. The program only support n>27 and n<160 and only support k>= 224 or larger, depends a bit on the n and m I think. I checked all factors I can get the program to work with, which was 29<=n<=149 and most of the factors with k>107.

Last fiddled with by ATH on 2012-09-18 at 02:12

 2012-09-18, 02:52 #5 LaurV Romulan Interpreter     "name field" Jun 2011 Thailand 3·11·13·23 Posts At least, is a very good sign that it finds them (for n>m-2, if we name Fm and k*2^n+1, I wondered if it will find factors if n>m-2 strictly). (stupid question: are the third a new factor, or you tested to see if it re-finds an older factor?) edit: @Gerbicz: I hope you wanted to be ironical. This is not a serious bug, as long as we have the right k, finding n is piece of cake... and about the program having the factors in a table, are you implying that George is a charlatan or what? I really hope you just joked! Last fiddled with by LaurV on 2012-09-18 at 02:55
 2012-09-18, 03:04 #6 Prime95 P90 years forever!     Aug 2002 Yeehaw, FL 2×3×5×7×37 Posts This is almost certainly a bug in the aptly named "dumb num" routines in tf_validate.h
 2012-09-18, 03:56 #7 Prime95 P90 years forever!     Aug 2002 Yeehaw, FL 171328 Posts dumb num fixed in 0.24. If you find a new Fermat factor in 0.23 and earlier, we'll need to verify which Fermat number the factor really divides.
2012-09-18, 15:47   #8
flashjh

"Jerry"
Nov 2011
Vancouver, WA

1,123 Posts

Quote:
 Originally Posted by Prime95 dumb num fixed in 0.24. If you find a new Fermat factor in 0.23 and earlier, we'll need to verify which Fermat number the factor really divides.
Have you posted .24 source code yet?

2012-09-18, 15:57   #9
Prime95
P90 years forever!

Aug 2002
Yeehaw, FL

2×3×5×7×37 Posts

Quote:
 Originally Posted by flashjh Have you posted .24 source code yet?
Not yet. Let's wait a few days to see if any other bugs are reported.

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