20200520, 20:03  #1 
Mar 2019
67 Posts 
GMPECM with gwnum failure
Got this failure today. I cannot tell if this is a bug in GMPECM or GWNUM, or some combination?
Code:
$ echo "(7^2048+1)/4119427741479153633869060968771666377359362"  ./ecm v c 100 11e7 GMPECM 7.0.4 [configured with GMP 6.2.0, GWNUM 29.8, enableasmredc] [ECM] Tuned for x86_64/k8/params.h Due to incompatible licenses, this binary file must not be distributed. Input number is (7^2048+1)/4119427741479153633869060968771666377359362 (1689 digits) Found number: 1*7^2048 + 1 Using mpz_mod Using B1=110000000, B2=900514153782, polynomial Dickson(30), sigma=0:16110665023593047747 dF=199680, k=2, d=2081310, d2=13, i0=40 Expected number of curves to find a factor of n digits: 35 40 45 50 55 60 65 70 75 80 34 133 600 3065 17462 108584 733594 5340128 4.2e+07 3.5e+08 Using gwnum_ecmStage1(1, 7, 2048, 1, 110000000, 1) ecm: Fgw.c:399: gw_ecm_stage1: Assertion `siz_x <= (unsigned long) ((gw_x)>_mp_alloc)' failed. Aborted 
20200520, 20:43  #2 
P90 years forever!
Aug 2002
Yeehaw, FL
2×5×691 Posts 
I believe the bug is in Fgw.c
The lines: Code:
mpz_init2 (gw_x, (gw_n+1)*gw_log_2(gw_b)+64); mpz_init2 (gw_z, (gw_n+1)*gw_log_2(gw_b)+64); This is an overkill solution: Code:
mpz_init2 (gw_x, (gw_n+1)*(gw_log_2(gw_b)+1)+64); mpz_init2 (gw_z, (gw_n+1)*(gw_log_2(gw_b)+1)+64); 
20200520, 22:37  #3  
Mar 2019
67_{10} Posts 
Quote:
The fix does seem to be working locally. I don't know if the GMPECM developers monitor this forum; perhaps they should be made aware of the proposed fix? 

20200521, 09:49  #4 
P90 years forever!
Aug 2002
Yeehaw, FL
2·5·691 Posts 
The developers report the problem is fixed in revision 3084

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