20150102, 13:45  #45 
"Carlos Pinho"
Oct 2011
Milton Keynes, UK
2^{3}×641 Posts 
Do you guys know if mprime still uses the old RES? If not I made a test on a few candidates that a few months ago had the same issue as posted by "AG5BPilot".
First result of the candidate was using the latest mprime version under linux with an avx processor. Second result for the same candidate was run under windows with avx2.0 processor. RES don't match so I ask "using a slower, more reliable method" means using a different FFT length? Will it cause different RES? Code:
5*2^48616841 is not prime. RES64: 070B09EDC7FC155B. 5*2^48616841 is not prime. LLR Res64: CB26DEA1F0727791 Time : 4924.949 sec. 5*2^48624541 is not prime. RES64: AFC485010F1E4C9C 5*2^48624541 is not prime. LLR Res64: CC06F5511F59EC44 Time : 4943.288 sec. 5*2^48539641 is not prime. RES64: E19D921AD6DECF13. 5*2^48539641 is not prime. LLR Res64: BD204C54267596C2 Time : 4897.556 sec. 5*2^48551081 is not prime. RES64: F1900AB229F963A8 5*2^48551081 is not prime. LLR Res64: 0A6441632949AA97 Time : 4927.116 sec. 5*2^48476221 is not prime. RES64: 72E5D1B0411002F8 5*2^48476221 is not prime. LLR Res64: 397F6DD1CB898DA3 Time : 4882.750 sec. 5*2^48476501 is not prime. RES64: 9DC9B1C69A7696CF. 5*2^48476501 is not prime. LLR Res64: 382A1A7D2D638E94 Time : 4916.712 sec. Carlos Last fiddled with by pinhodecarlos on 20150102 at 13:51 
20150102, 15:51  #46 
Dec 2011
New York, U.S.A.
97 Posts 
My issue turned out to not be an issue at all  the nonmatching residue was a hardware error on the AMD. The AVX (or FMA) results were correct.

20150212, 12:56  #47 
Dec 2011
New York, U.S.A.
141_{8} Posts 

20150212, 17:20  #48 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
19·23^{2} Posts 
No news.

20150323, 22:04  #49 
"Mark"
Apr 2003
Between here and the
2^{4}×3×5×29 Posts 
I have run a test with pfgw 3.7.8 (on 1024*3^1877301+1) and can report that I have reproduced the primality test results. a1 and a2 yield composite, but a3 yields prime. I'm going to run a PRP test with the different settings for a and compare the results. If they do differ, then I will run a test with different values of k to see if that have an impact on the results. With k being a power of 2, I wonder if that has any bearing on the results. I will then change to use gwsquare_carefully for every step.
If the PRP test results are the same regardless of a, then it could be problem with pfgw, but since LLR has the same problem and uses a different algorithm, it points to gwnum as the possible culprit. 
20150324, 00:38  #50 
"Mark"
Apr 2003
Between here and the
2^{4}×3×5×29 Posts 
Hmmm. The PRP test came back as 3PRP without specifying a.
I'm running a test that will do error checking on all steps and I'm running a test with a 32bit build of pfgw. Can someone please answer this question? Is LLR exhibiting the same problem on the primality test of this number? 
20150324, 01:01  #51 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
19×23^{2} Posts 
I've written up all that I've gathered at the UTM page (C.C. didn't try to mess with a values and marked it 'External', so I had to write some explanation). What you wrote agrees with what I observed; in particular PRP test is immune to the bug at default (a0).
In LLR, I didn't try to force "PRP only" but such option exists afair, so I guess it can be done. I'll try both the latest (.14) and then current (.13) versions. _______________________ ...ok, that's where "FBase=" parameter "goes" in LLR! I figured it out by running ./sllr64 d w4 oForcePRP=1 oFermatBase=7 oPBase=5 oFBase=11 c.npg > & 4/out & and in that directory ("4/"), the PRP base is 11. Output: Starting probable prime test of 1024*3^1877301+1 Using allcomplex AVX FFT length 240K, Pass1=1280, Pass2=192, a = 11 1024*3^1877301+1 is base 11Strong Fermat PRP! (895704 decimal digits) Time : 5270.521 sec. Starting Lucas sequence Using allcomplex AVX FFT length 240K, Pass1=1280, Pass2=192, P = 5, Q = 3 ... In directory with default (FBase=3): Starting probable prime test of 1024*3^1877301+1 Using allcomplex AVX FFT length 240K, Pass1=1280, Pass2=192, a = 3 1024*3^1877301+1 is base 3Strong Fermat PRP! (895704 decimal digits) Time : 5347.999 sec. Starting Lucas sequence Using allcomplex AVX FFT length 240K, Pass1=1280, Pass2=192, P = 5, Q = 3 ... Last fiddled with by Batalov on 20150324 at 03:11 
20150324, 11:42  #52 
"Mark"
Apr 2003
Between here and the
2^{4}×3×5×29 Posts 
32bit pfgw returned composite on the N1 test. The one with error checking every step is still running after 8 hours.

20150324, 16:55  #53 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
23503_{8} Posts 
The PRP tests by LLR finished. They are threefold (strongFermat, Lucas and Frobenius) and they all seem to pass (in test bases 3 and 11 and with two FFT sizes AVX FFT length 240K and AVX FFT length 256K)
Code:
Starting probable prime test of 1024*3^1877301+1 Using allcomplex AVX FFT length 240K, Pass1=1280, Pass2=192, a = 11 1024*3^1877301+1 is base 11Strong Fermat PRP! (895704 decimal digits) Time : 5270.521 sec. Starting Lucas sequence Using allcomplex AVX FFT length 240K, Pass1=1280, Pass2=192, P = 5, Q = 3 1024*3^1877301+1 is strongFermat and Lucas PRP, Starting Frobenius test sequence Using allcomplex AVX FFT length 240K, Pass1=1280, Pass2=192, Q = 3 1024*3^1877301+1 is strongFermat, Lucas and Frobenius PRP! (P = 5, Q = 3, D = 13) Time : 21495.646 sec. (Factorized part = 100.00%) # this run with oFFT_Increment=1 Starting probable prime test of 1024*3^1877301+1 Using allcomplex AVX FFT length 256K, Pass1=256, Pass2=1K, a = 11 1024*3^1877301+1 is base 11Strong Fermat PRP! (895704 decimal digits) Time : 5303.134 sec. Starting Lucas sequence Using allcomplex AVX FFT length 256K, Pass1=256, Pass2=1K, P = 5, Q = 3 1024*3^1877301+1 is strongFermat and Lucas PRP, Starting Frobenius test sequence Using allcomplex AVX FFT length 256K, Pass1=256, Pass2=1K, Q = 3 1024*3^1877301+1 is strongFermat, Lucas and Frobenius PRP! (P = 5, Q = 3, D = 13) Time : 22297.196 sec. (Factorized part = 100.00%) Starting probable prime test of 1024*3^1877301+1 Using allcomplex AVX FFT length 240K, Pass1=1280, Pass2=192, a = 3 1024*3^1877301+1 is base 3Strong Fermat PRP! (895704 decimal digits) Time : 5347.999 sec. Starting Lucas sequence Using allcomplex AVX FFT length 240K, Pass1=1280, Pass2=192, P = 5, Q = 3 1024*3^1877301+1 is strongFermat and Lucas PRP, Starting Frobenius test sequence Using allcomplex AVX FFT length 240K, Pass1=1280, Pass2=192, Q = 3 1024*3^1877301+1 is strongFermat, Lucas and Frobenius PRP! (P = 5, Q = 3, D = 13) Time : 23277.896 sec. (Factorized part = 100.00%) 
20150324, 19:19  #54 
"Mark"
Apr 2003
Between here and the
2^{4}×3×5×29 Posts 

20150324, 19:50  #55 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
19·23^{2} Posts 
I may revive the debugging path that I'd dropped around New Year. That is, in short, following on a hunch that something is happening in the very last step, I think. I've attached the almost done computation's savefile (but this is for LLR). You may want to create a similar .pfr file (with some manipulations to instruct the code to dump it exactly at the iteration you want, if needed), and try something similar.

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