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Old 2004-05-25, 08:46   #1
Boulder
 
May 2003

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Default 28.0M - 28.01M to 65 bits for starters

Hi,

I've started factoring the range to 65 bits. I'll probably go deeper as soon as the round is complete and I'll keep you posted.
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Old 2004-07-08, 12:33   #2
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Now going at M28005269, only one exponent with a factor found so far
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Old 2004-07-08, 14:20   #3
ThomRuley
 
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One exponent? That's great! One less exponent for LL testing. Your couple hours of factoring just saved the project about a month of LL. Great job.
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Old 2004-07-08, 17:15   #4
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Well, I would have expected a couple but then again, aren't the factors more rare when you TF the exponents 'deeper' ?
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Old 2004-07-08, 21:42   #5
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Consider that by factoring up to 55bits, many many factors have been removed (maybe 50% of all exponents are eliminated by factoring to 55bit). What you are doing is squeezing a few more out before P-1 will get ~1% of the remaning. All of this proves that it is not prime and saves much time in the hunt.
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Old 2004-07-09, 04:31   #6
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All factors are good - they save on LL tests! One factor is well within what's expected: if I'm close in reckoning that you had TF'd 114 exponents from 2^64 to 2^65, you had 30% chance of one factor and 27% chance of two factors.

According to prime95's help file, the chance of finding a factor for an exponent between 2^b & 2^(b+1) is approximately 1/b. The killer is that the time taken doubles. It is very much worth it though - TF will still be cost-effective up to 2^67 for these exponents.
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Old 2004-07-09, 05:29   #7
Boulder
 
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Thanks for the explanations, guys.

I've been thinking about starting TF'ing the remaining exponents to 2^66 as soon as 2^65 is finished but I'm not sure how far I would get before the range will be in PrimeNet. Since I do some real work on the computer (a P4-2.76GHz), it's very hard to estimate the time needed. At the moment the time per exponent is a bit over three hours if I'm not doing anything special. If I shut down all the other processes the time might go down to two and a half hours so it would take about 5-7 hours per exponent when TF'ing to 2^66.

Guess I'll just go with the range as long as I can

EDIT: By the way, is it that TF'ing to 2^64 is not as effective on a SSE2-capable machine as to 2^65?

Last fiddled with by Boulder on 2004-07-09 at 05:37
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Old 2004-07-09, 07:34   #8
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Above 2^64, SSE2 gives a big advantage - I don't know by how much.

Below 2^62, Athlons outpace P4s apparently because of some fancy coding that does two-for-one somehow. I don't know any more about why it is (and even this might be wrong!) or where non-SSE2 intel cpus fit in, but I do know that for TF below 2^62 an Athlon XP at 1533MHz is way faster than a P4 at 1800MHz.

In between... not sure.
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Old 2004-07-09, 10:40   #9
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These were some tests I ran a while back:

Time taken to complete 14366959 to 0.98%

Code:
To Bit  On PII 450      On P4 2533      Improv  On 1333TB       Improv

59      6               2.5             2.4     1.85            3.25
60      12              5               2.4     3.7             3.25
61      24              10              2.4     7.4             3.25
62      48              20              2.4     14.8            3.25
63      170             37.5            4.5     51              3.33
64      340             75              4.5     102             3.33
65      1540            180             8.5     480             3.21

Last fiddled with by garo on 2004-07-09 at 10:41
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Old 2004-11-06, 11:18   #10
Boulder
 
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Hi all,

I had an HD crash two months ago and lost a lot of work. I'm now attempting to factor the range to 2^65 before it hits the network, but can't promise anything. I remember seeing at least one number being factored so there's some motivation at least.

Please notify me if the range goes out, I might not remember to log in often.
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Old 2004-11-18, 15:27   #11
Boulder
 
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OK, I'll release the range as it should soon enter PrimeNet. I emailed the results to George, I nailed that one candidate which I remembered getting factored
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