- **Software**
(*https://www.mersenneforum.org/forumdisplay.php?f=10*)

- - **Yet another LLR bug**
(*https://www.mersenneforum.org/showthread.php?t=15272*)

Yet another LLR bugI have observed the following in LLR version 3.8.5:
When testing 10^500+961, LLR tells me: [CODE] Starting probable prime test of 10^500+961 10^500+961 is not prime, although base 3-Fermat PSP!! Time : 32.815 ms. [/CODE]but 10^500+961 has been certified prime using Primo! Nugget |

[QUOTE=nuggetprime;252928]I have observed the following in LLR version 3.8.5:
When testing 10^500+961, LLR tells me: [CODE] Starting probable prime test of 10^500+961 10^500+961 is not prime, although base 3-Fermat PSP!! Time : 32.815 ms. [/CODE]but 10^500+961 has been certified prime using Primo![/QUOTE] LLR cannot prove primality for this number. If anything, the message is inaccurate. |

Normally,LLR outputs when it can't prove a number prime:
[CODE]Starting probable prime test of 2^21954+77899 2^21954+77899 is base 3-Strong Fermat PRP! Time : 1.728 sec. Starting Lucas sequence 2^21954+77899 is Lucas PRP, Starting Frobenius test sequence 2^21954+77899 is Frobenius PRP! (P = 4, Q = 2, D = 8) Time : 6.928 sec. [/CODE] But for 10^500+961 it doesn't run a Lucas or Frobenius sequence and instead says the number is not prime. So I think it really is a bug. |

Another problem[CODE]./llr-3.8.5 -d -q5*10^19737+3
Starting probable prime test of 5*10^19737+3 5*10^19737+3 is base 3-Strong Fermat PRP! Time : 12.733 sec. Starting Lucas sequence Speicherzugriffsfehlerlength 4K, P = 4, Q = 2 [/CODE] "Speicherzugriffsfehler" means that it SEGV'ed here,trying to compute the Lucas sequence. |

BUMPed.
Also forwarded to Jean Penne. |

The two bugs on LLR 3.8.5 are fixed!Hi,
These two bugs are now fixed : - For 10^500+961, it is really a bug of the strong Fermat PRP code in the Llr.c file. It will be fixed in the Development version ; here is the correct behaviour : Starting probable prime test of 10^500+961 Using all-complex FFT length 192, a = 3 10^500+961 is base 3-Strong Fermat PRP! Time : 121.052 ms. Starting Lucas sequence Using all-complex FFT length 192, P = 5, Q = 3 10^500+961 is strong-Fermat and Lucas PRP, Starting Frobenius test sequence Using all-complex FFT length 192, Q = 3 10^500+961 is strong-Fermat, Lucas and Frobenius PRP! (P = 5, Q = 3, D = 13) Time : 72.780 ms. For 5*10^19737+3, it is a gwnum problem : gwnum chooses a full-complex 4K FFT, which seems to be too small, and causes a segmentation fault after a few iterations... And the test works if I force the program to choose the third next larger FFT! Here is the result, using the uncorrected LLR on Linux : ~/llr385src/linuxllr $ ./llr -a3 -oVerbose=1 -oLucasPRPtest=1 -oFFT_Increment=3 -d -q"5*10^19737+3" Starting Lucas sequence 5*10^19737+3 is Lucas PRP, Starting Frobenius test sequence 5*10^19737+3 is Frobenius PRP! (P = 4, Q = 2, D = 8) Time : 127.685 sec. The chosen FFT is then Zero padded 10K... Note : The -oLucasPRPtest=1 is necessary here, to skip the Fermat test which reset the FFT increment at its completion... This drawback will be corrected in the Development version. I shall release it soon... I shall also warn George about this gwnum problem. Best Regards, Jean |

[QUOTE=Jean Penné;254001]Hi,
These two bugs are now fixed : - For 10^500+961, it is really a bug of the strong Fermat PRP code in the Llr.c file. It will be fixed in the Development version ; here is the correct behaviour : Starting probable prime test of 10^500+961 Using all-complex FFT length 192, a = 3 10^500+961 is base 3-Strong Fermat PRP! Time : 121.052 ms. Starting Lucas sequence Using all-complex FFT length 192, P = 5, Q = 3 10^500+961 is strong-Fermat and Lucas PRP, Starting Frobenius test sequence Using all-complex FFT length 192, Q = 3 10^500+961 is strong-Fermat, Lucas and Frobenius PRP! (P = 5, Q = 3, D = 13) Time : 72.780 ms. For 5*10^19737+3, it is a gwnum problem : gwnum chooses a full-complex 4K FFT, which seems to be too small, and causes a segmentation fault after a few iterations...[/QUOTE] I suspect that it might be CPU specific or specific to the 32-bit version. On 64-bit MacIntel, pfgw chooses the 4K FFT and it runs without a problem. Granted pfgw and llr use different code. I would have to try with 64-bit llr on MacIntel to know for certain. |

[QUOTE=Jean Penné;254001]
For 5*10^19737+3, it is a gwnum problem : gwnum chooses a full-complex 4K FFT, which seems to be too small, and causes a segmentation fault after a few iterations... And the test works if I force the program to choose the third next larger FFT! [/QUOTE] What system is this? A PRP test using 32-bit Windows Prime95 on a Core 2 works using a 4K FFT. |

Proble with c!=1 and IBDWT...[QUOTE=Prime95;254015]What system is this? A PRP test using 32-bit Windows Prime95 on a Core 2 works using a 4K FFT.[/QUOTE]
Hi, I can now add some precisions about this problem : -It occurs each time I am running a Lucas PRP test on a k*b^n+c number with c != 1 AND a full complex FFT is chosen. - If I force a larger FFT, the test works as soon as Zero padded is chosen. - It works also if I force generic reduction. - No matter if the base b is two or not... - Surprisingly, the simple strong Fermat PRP test (which uses only gwsquare) works always! For the Lucas test, I get a segmentation fault on these two systems : On Windows 2000 and VC 6.0 : CPU Information: Intel(R) Pentium(R) 4 CPU 2.53GHz CPU speed: 2533.16 MHz CPU features: RDTSC, CMOV, PREFETCH, MMX, SSE, SSE2 L1 cache size: 8 KB L2 cache size: 512 KB On Linux with 32 bit gcc and gwnum library : CPU Information: AMD Athlon(tm) 64 Processor 3700+ CPU speed: 2199.85 MHz CPU features: RDTSC, CMOV, PREFETCH, MMX, SSE, SSE2 L1 cache size: 64 KB L2 cache size: 1024 KB I hope it will help... Regards, Jean |

I was able to reproduce this on Windows (in LLR). The problem is triggered by this line:
gwfftmul (gwdata, tmp2, tmp4); /* Compute s*random */ in gwmul_carefully. Both tmp2 and tmp4 are good values. |

Ugh, I cannot reproduce in Prime95 using my QA code that calls every gwnum routine.
I did download and compile the LLR source, but don't know how to use it. Can you upload an input file that exhibits the problem? Thanks. |

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