George,
I think I've found two bugs in Prime95 or, at least, serious
misfeatures. I don't know whether they've been fixed in more recent
releases but as I'm using the program in a rather creative manner I
suspect not. The Mersenne list is Cc:ed so that if anyone else wishes
to use your program in this way they will be aware of the problems and
take appropriate countermeasures.
Bug 1: A factor specified in lowm.txt or lowp.txt which is more than a
hundred or so decimal digits is not read correctly and is incorrectly
reported as not dividing the M or P number being factored. The exact
length at which it fails wasn't determined directly but it's around that
size.
Bug 2: If worktodo.ini contains two lines specifying ECM work to be
done, and a factor is found of the first number, the worktodo.ini file
is truncated to zero size and Prime95 halts. In my opinion it's a
misfeature that the program doesn't append the new factor to
low{m,p}.txt and continue with the remaining curves on that integer but
I accept that may not be what everyone wants. Wiping out all remaining
lines *is* a bug in my opinion.
Background:
The number 2^64695-2^15+1 is a Miller-Rabin pseudoprime. It could be
proved prime by completely factoring 2^15*(2^64680-1). The latter
number has a lot of algebraic factors, including M32340 and P32340.
There are so many algebraic factors that even tiny B1 limits for the ECM
and P-1 algorithms find very large composite factors.
Regards,
Paul
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