20150423, 11:42  #1 
Apr 2013
Germany
138_{16} Posts 
odd segmentation fault
Hi,
I have an odd segmentation fault with the current yafu from svn (r342). Here is the problem: Code:
./yafu "factor(123456789009876543211234567890098765432112345678900987654321333)" fac: factoring 123456789009876543211234567890098765432112345678900987654321333 fac: using pretesting plan: normal fac: using tune info for qs/gnfs crossover div: primes less than 10000 rho: x^2 + 3, starting 10000 iterations on C60 rho: x^2 + 2, starting 10000 iterations on C60 rho: x^2 + 1, starting 10000 iterations on C60 nfs: couldn't find special form Speicherzugriffsfehler running the same number using siqs directly gives me the factors: Code:
$ ./yafu "siqs(123456789009876543211234567890098765432112345678900987654321333)" starting SIQS on c60: 370741108137767397030734438108404700997334371408111074037001 using sse4.1 with med_sieve using sse4.1 with med_sieve using sse2 with tdiv_medprimes ==== sieving in progress ( 4 threads): 3552 relations needed ==== ==== Press ctrlc to abort and save state ==== 3699 rels found: 1805 full + 1894 from 16596 partial, (36425.79 rels/sec) SIQS elapsed time = 0.5595 seconds. ***factors found*** P1 = 3 P1 = 3 P2 = 37 P17 = 28596344498792569 P44 = 12964632880031966906598999600889772386272529 1 I compiled yafu with: Code:
make x86_64 USE_SSE41=1 NFS=1 
20150423, 16:07  #2 
Jun 2003
2^{2}·3·439 Posts 
Apparently on this tiny number, yafu wants to do nfs, not SIQS. Perhaps some setting is preventing selection of siqs. Time to retune?

20150423, 17:00  #3 
Apr 2013
Germany
2^{3}·3·13 Posts 
This is my current tune_info:
Code:
tune_info=Intel(R) Core(TM) i54460 CPU @ 3.20GHz,LINUX64,1.18706e05,0.204099,0.324344,0.0997272,97.8757,3199.98 The segfault also happens with C97 from FDB but not with a C98 (which is my crossover point exactly) Here is with a C97 (should use siqs): Code:
./yafu "factor(1346890506266962133588620189606901951267040142442737102201365939343891347202689878898996138897973)" fac: factoring 1346890506266962133588620189606901951267040142442737102201365939343891347202689878898996138897973 fac: using pretesting plan: normal fac: using tune info for qs/gnfs crossover div: primes less than 10000 rho: x^2 + 3, starting 10000 iterations on C97 rho: x^2 + 2, starting 10000 iterations on C97 rho: x^2 + 1, starting 10000 iterations on C97 nfs: couldn't find special form Speicherzugriffsfehler Code:
./yafu "factor(19368533560477550795984783104796436186904996663790040806670180091266794230924763204502549642766057)" fac: factoring 19368533560477550795984783104796436186904996663790040806670180091266794230924763204502549642766057 fac: using pretesting plan: normal fac: using tune info for qs/gnfs crossover div: primes less than 10000 rho: x^2 + 3, starting 10000 iterations on C98 rho: x^2 + 2, starting 10000 iterations on C98 rho: x^2 + 1, starting 10000 iterations on C98 nfs: searching for brent special forms... nfs: searching for homogeneous cunningham special forms... nfs: searching for XYYXF special forms... nfs: couldn't find special form pm1: starting B1 = 150K, B2 = gmpecm default on C98 ecm: 30/30 curves on C98, B1=2K, B2=gmpecm default ecm: 74/74 curves on C98, B1=11K, B2=gmpecm default ecm: 216/216 curves on C98, B1=50K, B2=gmpecm default, ETA: 0 sec pm1: starting B1 = 3750K, B2 = gmpecm default on C98 ecm: 404/404 curves on C98, B1=250K, B2=gmpecm default, ETA: 0 sec c nfs: commencing nfs on c98: 19368533560477550795984783104796436186904996663790040806670180091266794230924763204502549642766057 nfs: searching for brent special forms... nfs: searching for homogeneous cunningham special forms... nfs: searching for XYYXF special forms... nfs: couldn't find special form nfs: commencing polynomial search over range: 8192  8442 nfs: commencing polynomial search over range: 8692  8942 nfs: commencing polynomial search over range: 8442  8692 nfs: commencing polynomial search over range: 8942  9192 
20150423, 20:23  #4 
"Ben"
Feb 2007
2·11·163 Posts 
I don't have a complete answer just yet. However, the message doesn't necessarily indicate that it is doing NFS... just that it tried to find a NFS form. I added this check early in the factor algorithm because if there is an NFS form then the amount of ECM scheduled is reduced.
This helps pinpoint where the problem might be but I won't have time to look for it for the next few days at least. 
20150909, 19:38  #5 
Aug 2002
3×83 Posts 
It may be worth mentioning that I encountered a similar issue when yafu was run on the small, but not unNFSably small, composite 194417753850401901402207205967096376638960217120756813979312551274352249332562607796084956616283 from my current aliquot work. It was called by the aliqueit binary. Running ./yafu 'nfs(num)' directly from the shell worked fine.

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