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GIMPS newsletter #17, 4 October, 1999

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The Mersenne Newsletter, issue #17 October 4, 1999


1. New email address for George,
2. Faster version 19 now available
3. What's new in version 19?
4. Thanks
5. Note on estimated completion dates
6. GIMPS and the $100,000.00 EFF award

1. New email address
My email address is Please update your records.
My old magicnet email address will not work much longer.

2. Faster version 19 now available
Version 19 is now available and it is up to 10% faster!
Here are some sample per-iteration timings from my PII-400:

Exponent V18 timing V19 timing
-------- ---------- ----------
3500000 0.104 0.0982 5.6% faster
4200000 0.1266 0.1193 5.8% faster
7000000 0.2292 0.2107 8.1% faster
8200000 0.278 0.2520 9.4% faster

You can get the new version at,htm
To upgrade, stop and exit the current version. Optionally
make a backup of the directory. Unzip the new version on top of the
old version. Start the new version of the program.

Save files are upward compatible from previous versions but not
backward compatible. Thus, if you are in a dual-boot environment
make sure you upgrade the Windows and Linux versions at the same time.

3. What's new in version 19?

1) Faster - in some cases as much as 10% faster!. The FFTs were recoded
for improved memory and TLB efficiency. Furthermore, optimizations
specific to the Pentium Pro and later processors were added.
2) New FFT lengths. The program can now test exponents as large as
79.3 million. Also, smaller FFT lengths are supported for use in
ECM and P-1 factoring.
3) More conservative FFT breakpoints. This could actually result in
a few exponents being slower to test in this version. However, the
chance of a fatal rounding error has been reduced.
4) P-1 factoring has been added. Although it is not very practical for
large exponents because of a slow GCD routine, it can be used to
find new factors of exponents below a few million or so.
5) ECM can now run on large exponents. Once again, the slow GCD routine
and high memory requirements might make this impractical for large
6) ECM and P-1 factoring now support save files. Very handy on lengthy runs.
The count of completed ECM curves is maintained in the save file instead
of the worktodo.ini file.
7) ECM and P-1 factoring lets you specify the amount of memory to use.
In some cases, more memory can improve execution speed slightly.
8) A bug in guessing the CPU speed on initial install has been fixed.
9) The preferences dialog now has an option to pause prime95 when a laptop
is running on its battery.
10) Error checking has been improved slightly.
11) Factoring is now "layered". That is, prime95 now factors to 2^50, then
2^51, 2^52, and so forth up to the appropriate limit. The factoring
output lines have been changed to show percent complete in the current
12) A bug in running two or more self or torture tests in the same directory
has been fixed.
13) Trial factoring above 2^64 is now supported.
14) More trial factoring is now done to take into account the cost of
15) Title now contains percent complete when LL testing. By default, the
percent complete value is now displayed to 2 decimal places. You can
change this by setting PercentPrecision in prime.ini to a value
between 0 and 6.
16) Affinity and service name settings moved from prime.ini to local.ini file.
Prime95 will automatically move these settings for you.
17) An option to get only 10,000,000 digit numbers to run primality tests
on has been added to the Test/Primenet dialog box. See for rules on claiming the EFF award
for finding a 10,000,000 digit prime.
18) The Advanced/Clear primes menu choice has been deleted.
19) The prime95 icon turns yellow when the program is idle. After an
error such as ILLEGAL SUMOUT, the icon will blink for 10 seconds.
20) The User Information dialog box allows you to request newsletters and
form a team user ID where the team members cannot alter the team name.
21) A bug in the reporting of error counts in the results.txt file has
been fixed.
22) The server can now broadcast important messages to the prime95 client.
Prime95 will blink the icon until prime95 is activated and then it will
display the message.
23) A computer ID will be generated for computers that do not have one. If
you want to assign your own computer ID, please try to make each
computer ID using the same user ID unique.

4. Thanks
I'd like to thank the excellent work of the QA team. They located
many bugs, bringing you a higher quality beta. The QA team included
Ken Kriesel, Brian Beesley, Tom Cage, Jean-Yves Canart, Bryan Fullerton,
Marc Getty, Steinar H. Gunderson, Eric Hahn, Alex Healy, Paul Landon,
Greg McIntyre, Lawrence Murray, Paul Victor Novarese, Ethan M. O'Connor,
Rick Pali, Shane Sanford, Brian Schroeder, Gordon Spence, Joth Tupper,
Guillermo Ballester Valor, David Willmore, and Lucas Wiman.

And, of course, thanks to Scott Kurowski's team at for the
v19 enhancements to the PrimeNet server.

5. Note on estimated completion dates
The timings in version 19 have been recalibrated to my PII-400 instead
of my old, deceased P-90.

What does that mean? The short explanation is that you should not
initially trust the estimates given in Test/Status. Over time these
estimates will become accurate again.

Why is this? When version 18 estimated my PII-400's speed it underestimated
by 40%. Over time, the RollingAverage value in local.ini grew to 1400
to compensate for the poor guess and give accurate estimates in Test/Status.
In version 19, the program accurately guesses my PII-400's speed and
applying the rolling average of 1400 makes it bring in the expected completion
dates by 40%. It won't take too long for the rolling average to come
down to close to 1000 -- or you can edit your local.ini file my hand and
set the RollingAverage to 1000. Also changing you CPU type in Test/CPU
will reset the RollingAverage to 1000.

6. GIMPS and the $100,000 EFF award
The Electronic Frontier Foundation is offering a $100,000 award to
the first group to find a ten million digit prime number. The details
of how GIMPS will handle this award is at

Fair warning: A 500 MHz PC will take a full year to test a single exponent
with only 1 chance in 250,000 of finding a prime number.


George Woltman


Scott Kurowski &, Inc.