20030620, 15:33  #1 
Sep 2002
2×131 Posts 
After a factor is found it keeps on going
Hi George,
When I use FactorOverride, even if a factor is found, prime95 keep on going up to the override. I don't know if it's a bug or if it was intentionnally added. I heard of someone reporting 2 factors on the same number. I'm using 23.4.1 Joss 
20030620, 22:06  #2 
Jan 2003
far from M40
5^{3} Posts 
Hi, Joss!
AFAIK, this is due to the fact that Prime95 doesn't go through the factor  candidates in their natural order. So, if a factor is found, Prime95 checks smaller leftovers to ensure that there aren't any factors below that. Nevertheless, finding a factor below e.g. 2^60 should ensure that Prime95 won't look for factors between 2^60 and 2^61. Benjamin 
20030621, 19:47  #3  
"Richard B. Woods"
Aug 2002
Wisconsin USA
2^{2}·3·641 Posts 
In the Prime95 module source code commonb.c, where it determines that trial factoring has found a factor is this comment:
Quote:


20040805, 06:45  #4 
"Mark"
Feb 2003
Sydney
3·191 Posts 
I'm not sure prime95 is working like that. For example, if I factor M29900009 from a very low limit to a FactorOverride of 60 or less, prime95 reports a 44bit factor 8938129290407. But if FactorOverride is 61 or more, it reports a 33 bit factor 7415202233 as well, which is the one in nofactor.
I stumbled across this because I became interested in hunting for missed factors, like in this thread. I experimented with looking for gaps in the distribution of known factors. Unfortunately large sections have many exponents where a factor is known but a smaller factor has been missed, which distorts the distribution. So I wanted to see if it was feasible to fix that first, at least up to a low bitlevel. 
20040806, 04:50  #5 
Sep 2003
2×179 Posts 
Yes, it appears to work exactly the opposite of what the comment says. If FactorOverride is 60 or less, it stops upon finding a factor, but if it is 61 or greater, it continues to check all lower possible factors in that bit range.

20040806, 13:42  #6 
P90 years forever!
Aug 2002
Yeehaw, FL
2×4,127 Posts 
I'll fix it next release. Thanks

20040807, 01:31  #7 
"Mark"
Feb 2003
Sydney
3×191 Posts 
Thanks, George!

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