20091123, 12:53  #1 
"Mark"
Apr 2003
Between here and the
2^{2}·7·223 Posts 
GMPECM Request
I would like to see a feature to disable the PRP testing of the cofactor. This would be used on projects such as the primorial and factorial searches on PrimeGrid. All we want to do is "knock out" the original number from PRP testing if it is composite thus finding a factor is all that we need to do. PRP testing the cofactor adds no value to the project and can actually take longer than that PRP test for the original number (presuming GMP's PRP test is used).

20091123, 13:23  #2 
"Nancy"
Aug 2002
Alexandria
2,467 Posts 
This can currently be done by configuring with enableshellcmd, and specifying a program that always returns true (exit code 0) to the prpcmd, for example:
ecm prpcmd /bin/true [...] That way GMPECM thinks the cofactor is prime and stops trying to factor it. Code:
echo "2^(2^9)+1"  ./ecm prpcmd /bin/true 1e3 GMPECM 6.3 [configured with GMP 4.3.0 and enableasmredc] [ECM] Input number is 2^(2^9)+1 (155 digits) Using B1=1000, B2=51606, polynomial x^1, sigma=3861836176 Step 1 took 5ms Step 2 took 6ms ********** Factor found in step 2: 2424833 Found probable prime factor of 7 digits: 2424833 Probable prime cofactor (2^(2^9)+1)/2424833 has 148 digits 
20091123, 14:02  #3  
"Mark"
Apr 2003
Between here and the
14144_{8} Posts 
Quote:


20091123, 14:37  #4 
Jun 2003
Ottawa, Canada
491_{16} Posts 
If they added a feature to the code to do that, you would still have to rebuild GMPECM so either way you have another rebuild coming. The question is do you want to be able to get that functionality now or possibly sometime in the future?

20091123, 15:07  #5 
"Mark"
Apr 2003
Between here and the
2^{2}·7·223 Posts 
I can wait for it.

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