20100601, 09:42  #1 
Einyen
Dec 2003
Denmark
2×1,579 Posts 
Doublecheck always have shifted S0 value?
Sometimes I wonder if a normal LL test is sometimes registered as a doublecheck, without having shifted S0 starting value.
Cases like this: 36127031 (before) No factors below 2^67 P1 B1=435000, B2=9461250 Suspect LL 2F7D978FEC8E03__ by "Daniel Paoliello" Assigned LL testing to "ANONYMOUS" on 20090411 36127031 (now) No factors below 2^67 P1 B1=435000, B2=9461250 Verified LL 2F7D978FEC8E0313 by "Daniel Paoliello" Verified LL 2F7D978FEC8E0313 by "ANONYMOUS" on 20100509 History 2F7D978FEC8E03__ by "ANONYMOUS" on 20100509 Did Anonymous really start the test as a doublecheck back on 20090411 when there only was a suspect LL done? Or was it a normal LL that is now registered as a doublecheck. Last fiddled with by ATH on 20100601 at 09:43 
20100601, 10:27  #2 
"Richard B. Woods"
Aug 2002
Wisconsin USA
1E0C_{16} Posts 
Are you questioning the time span?
It seems normal enough that a suspect (because of error codes) firsttime LL would, after the doublecheck LL returns the same residue (without significant error codes), then be considered okay. (My understanding is that the S0 value is pseudorandomly shifted at the start of all LL runs, whether firsttime, DC, or later.) Last fiddled with by cheesehead on 20100601 at 10:31 
20100601, 11:05  #3  
Einyen
Dec 2003
Denmark
2×1,579 Posts 
Quote:
I thought it was only shifted when you did a DoubleCheck= in worktodo.txt instead of Test= Last fiddled with by ATH on 20100601 at 11:06 

20100601, 12:20  #4 
Aug 2002
Termonfeckin, IE
5314_{8} Posts 
I think there is a random shift applied at the start of every test. An exponent is only deemed doublechecked when there is a matching residue from two tests with different shift counts.

20100601, 15:28  #5 
A Sunny Moo
Aug 2007
USA (GMT5)
3×2,083 Posts 
What I always understood was that the S0 value was only randomized with DoubleCheck= and not with Test=. There seems to be quite a bit of uncertainty about how exactly this works, though, so it's quite possible I got this information from someone who in turn was mistaken. Perhaps George could clarify?
Also, one quick question: when S0 is shifted, do interim residues still match? If not, then that would mean that all of the bigiron verifications of newlyfound Mersenne primes (for which interim residues are compared throughout) actually use the same S0 and thus would not be as good a check as intended. 
20100601, 15:42  #6  
Jun 2003
5081_{10} Posts 
Quote:
Quote:
Well, even if the bigiron verifications used the same S0, it is in fact a much better independent test, since a) the code used is different and b) cpu architecture is different. It is only when the same code is used on the same architecture that we need to use the random shift concept. 

20100601, 15:46  #7  
P90 years forever!
Aug 2002
Yeehaw, FL
2^{2}×7×269 Posts 
Quote:
Quote:


20100601, 15:53  #8 
Jun 2003
5081_{10} Posts 

20100601, 16:18  #9  
"Richard B. Woods"
Aug 2002
Wisconsin USA
1E0C_{16} Posts 
Quote:
However, it's also true that when the pseudorandom shift was first introduced, there was a time period when all residues generated by older versions had not been shifted, so there were many cases in which a firstrun LL had no shift, then the DC run on the new version did have a shift. You may have received advice from someone confused about that. Since all DCs from older versions had no shift, there were also cases where both firstrun and DC had no shift. You may have noticed that all low exponents have had a third LL regardless of whether the first two matched. I think this was done after the shift was introduced, so that the third run would have a nonzero shift, for further verification. 

20100602, 07:41  #10 
Einyen
Dec 2003
Denmark
2×1,579 Posts 
That's good to know, it makes alot more sense then. So the DoubleCheck= is only to determine which category you get your credit for?
Allthough if you do a Test= and it turns out to doublecheck a suspect LL or normal LL, I guess you get doublecheck credit anyway? 
20100602, 10:56  #11  
Account Deleted
"Tim Sorbera"
Aug 2006
San Antonio, TX USA
17×251 Posts 
Quote:
Code:
Test=216091 DoubleCheck=216091 Code:
M216091 no factor to 2^39, Wd1: 021E0177 M216091 completed P1, B1=10000, B2=175000, Wd1: 05B5DAF7 M216091 no factor from 2^39 to 2^40, Wd1: 021E0177 M216091 is prime! Wd1: 8368E9FF,00000000 M216091 no factor to 2^38, Wd1: 021E0177 M216091 completed P1, B1=10000, B2=90000, Wd1: 05B68EFF M216091 no factor from 2^38 to 2^39, Wd1: 021E0177 M216091 is prime! Wd1: 8368E9FF,00000000 Last fiddled with by MiniGeek on 20100602 at 10:56 

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