Re: Mersenne: GIMPS accelerator?

2001-05-16 Thread Brian J. Beesley

On 15 May 2001, at 18:22, Daran wrote:

 GIMPS clients use the spare capacity of the primary processing resource within
 any computer:- the CPU(s).  But most modern PCs have another component capable
 of performing rapid and sophisticated calculations:- the GPU on the graphics
 accelerator.  Is there any way that the GPU can be programmed to perform GIMPS
 processing when otherwise not in use?

There are several practical difficulties:

(a) GPUs are usually 32-bit, single-precision hardware. Nothing more 
is needed for graphics displays. Running multiple precision 
arithmetic using floating-point FFT in single-precision hardware is 
not very effective; you need about 20 guard bits; with a single-
precision manitssa being 24 bits long, you don't have very much left 
to work with.

(b) GPUs run code from ROM. The system as a whole transfers data but 
not instructions from the main CPU to the GPU through the video card 
bus connectors. There is no easy way to change the code which runs 
the processor(s) on the graphics card.

(c) Even if the GPU was programmable from the system, there are so 
many different graphics card controller architectures that writing 
code that would work nearly universally would involve something close 
to an impossible amount of effort. And graphics cards keep changing, 
fast!

(d) Don't forget that running a LL test on a 10M exponent involves 
about 8 MBytes of data storage. This is not a serious problem given 
the amount of system memory available to most systems capable of 
completing a LL test on a 10M exponent in a reasonable time, but 
robbing 8 MBytes from the more limited memory available on most 
graphics cards might well be critical.


Regards
Brian Beesley
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Re: Mersenne: GIMPS accelerator?

2001-05-16 Thread Daran

-Original Message-
From: Gareth Randall [EMAIL PROTECTED]
To: [EMAIL PROTECTED] [EMAIL PROTECTED]
Date: 15 May 2001 23:36
Subject: Re: Mersenne: GIMPS accelerator?

Daran,

This is an interesting piece of lateral thinking that deserves to go further
than I think it actually does.

Thank you for taking me seriously.

Essentially, I'm not sure how the operations that a graphics card can
provide, such as line drawing, texture overlaying, raytraced light effects
etc, could be made to implement a LL test or FFT etc which would require
things like bit tests, conditioning branches and loops etc.

What you've listed are the functions of a graphics card, each of which will
have been implemented through the application of one or more primitive
operations.  For example, the function of mapping a set of co-ordinates in
3-space onto screen pixels will be implemented by a linear transformation,
which will itself be implemented through a number of scalar multiplications.

I'm wondering if it might be possible to access any of the available primitive
operations without having to invoke a specific card function.

AFAICS the problem requires affirmative answers to all of the following
questions.

1.Can the hardware theoretically do work useful to GIMPS?
2.Could this be done efficiently enough to be worthwhile?
3.Is it possible to program the hardware to do this work?
4.Would it be possible to read the results back from the card?
5.Is the available technical documentation sufficient for a programmer to
be able to implement this?
6.Would the implementation be acceptable to the user?
7.Are the prospective gains to the project worth the programming effort?

I suspect the answer to 1 is yes, given how simple the requirements are for a
set of primitive operations to be able to universally compute - the Turing
machine and Conway's life spring to mind.  But we wouldn't waste time
programming a hardware Turing machine to do LL tests, even if we had one.

An example of a user issue would be if the only way to program the card is to
'flash upgrade' the GPU's on-card firmware.  I wouldn't be willing to do that,
although I might consider installing a special GIMPS driver, so long as I
could uninstall again.

Conceivably additions could be done by superimposing textures and reading
back the resulting frame buffer, but these wouldn't be 64-bit precision
additions!

That's all you get with CPU integer arithmetic, but you can build longer ones
out of the shorter.

Maybe some form of matrix multiplication could be done by rotating textures
before superimposing? However, I think the resulting calculation efficiency
would be very poor, and may never achieve useful precision.

Could you not build an FFT out of Discrete Cosine Transforms?  Or build a
multiplication from DCTs in some other way?  Some cards have hardware support
for this.

Also, any code would be very hardware specific, and may only work if the
display was not displaying, say, a desktop.

Which would hit 'prospective gains' question hard, since it would not then be
useful on Windows machines.

However, if someone could implement it, it could provide the *ultimate* in
Mersenne related screen savers! What you'd see on the screen would be the
actual calculations themselves taking place before your eyes, and with no
overheads for displaying it either!

That I did not think of.

Yours,

=== Gareth Randall ===

Daran G.


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Re: Mersenne: Re: 26 exponents

2001-05-16 Thread Brian J. Beesley

On 15 May 2001, at 22:36, Steinar H. Gunderson wrote:

 On Tue, May 15, 2001 at 04:48:19PM +0100, Daran wrote:
 BTW what happens now when a first-time check, (or for that matter, if a
 double-check) discovers a new prime.  Surely this is checked immediately on
 the fastest machine available to the project, and not left to the vagaries of
 random allocation?
 
 It is run on a different architecture, with different software. The
 three first were (as far as I know) tested on Crays, 

Through the good offices of David Slowinski.

 while the 4th (M38
 (we think)) was tested on an Alpha machine with mlucas, as far as I
 remember.

Yes. DS couldn't help, for some reason, probably due to Cray having 
been bought out by Silicon Graphics.
 
 The idea is to completely eliminate any possibility of a persistent
 program or hardware bug :-)

Plus, Prime95 didn't have the random shift code which allows it to 
check its own results until after M37 was discovered; and the random 
shift code was rather new when M38(?) was discovered.

Another point - we're coming up to the second anniversary of the 
discovery of M38(?) - I think we're overdue to find another one!


Regards
Brian Beesley
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Re: Mersenne: GIMPS accelerator?

2001-05-16 Thread Brian J. Beesley

On 15 May 2001, at 22:46, Ken Kriesel wrote:

 Among others, I raised the question with George Woltman some time ago.
 I trust his judgment that his time is better spent elsewhere.

Agreed!
 
 However, I wonder if there might be some possibilities in trial factoring
 there.
 That would present the possibility of a factoring screensaver, and an FPU
 LLtest, running together on what is nominally a uniprocessor.
 
 Just speculation,

Nice idea (using the fact that trial factoring  screensaver would be 
almost pure integer work, whereas LL testing is almost pure FP) but 
with practical difficulties.

(1) To get any benefit, you're going to have to bind all that 
functionality into one thread - because if you are running more than 
one thread, the OS will schedule the threads independently, throwing 
away any benefit which might be gained by parallelism.

(2) I think there would be serious difficulties in coordinating code 
between LL testing (time per iteration almost constant, of the order 
of tens of millions of CPU cycles)  trial factoring (time per 
candidate very variable, and of the order of hundreds of CPU cycles). 
I've no idea at all as to how you would usefully squeeze in a 
screensaver too, but I do think that the code coordination neccessary 
to parallelize tasks in a single process thread would be very hard to 
achieve.

(3) Though trial factoring places almost no load on the system memory 
bus or the floating-point execution units, there are other potential 
bottlenecks within the CPU - in particular, the L1 instruction cache, 
instruction decoders, instruction pipelines, jump prediction tables  
spare registers (required for out-of-order execution) - which may 
well limit severely the amount of  factoring work which could be done 
in parallel with LL testing, without inflicting a significant 
performance penalty on LL testing. 

Given that trial factoring is well advanced, implementing a scheme 
which increases the trial factoring throughput of the project as a 
whole at the expense of LL testing throughput does not seem to be a 
good idea.

However, if anyone can provide the functionality that Ken suggests 
without impacting LL testing performance noticeably, I'll be just as 
grateful as everyone else!


Regards
Brian Beesley
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Re: Mersenne: Re: 26 exponents

2001-05-16 Thread Daran

-Original Message-
From: Brian J. Beesley [EMAIL PROTECTED]
To: Nathan Russell [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED] [EMAIL PROTECTED]
Date: 15 May 2001 23:57
Subject: Re: Mersenne: Re: 26 exponents

Actually I think that there may be a perceptual problem with many new
users in that they may give up as soon as they realize that a most
sense assignment is going to take several weeks to complete.
Unfortunately there seems to be no easy way to fix this!

I think this could be a significant problem.

I'm currently 46% of the way through double-checking M6193307, and I'm
expecting to complete it on 26 July.  Last time I dropped bellow 90 days
queued work, I requested a factorisation, just to see what the range was.  I
got M16065053, which I expect to complete on 6 September - nearly six weeks
to do the fastest possible assignment.  This doesn't bother me now - I
wouldn't be bothered if it took a year or more - but when I started, I was
keen to return a result.  OK, you might think a slow machine like mine would
be no great loss to the project, but I'm not going to have this abacus for
ever.

One improvement would be to credit people with work done each time they check
in, instead of only when they return a result.  That way they can see
themselves on the producer charts more or less immediately.

Another possibility would be to extend the project to search for something
else - there must be many other interesting number-theoretic questions
involving primes which are not currently being researched in depth, and which
could benefit from a distributed approach.  We already do this with
factorisations which do not contribute to the search for a Mersenne prime.
There must be many people who started off doing factorisations before moving
on to double-checks and first-time LLs.

[...]

 Perhaps clicking the 'give me the work that makes the most sense' box
 should immediately set the appearance of the others to the work that
 will be chosen, rather than simply graying them out.

Agreed.

Does the client 'know' the threshold performance level for double-checks and
factorisations?  If so, is it hard-coded, or does it get this information from
the server?  If hard-coded, then you have a problem with people continuing to
use older clients which tell them that it still makes 'most sense' to do
first-time checks, long after it has become more sensible to do double-checks
or factorisations.

Regards
Brian Beesley

Daran G.


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Re: Mersenne: ECM Question...

2001-05-16 Thread Alexander Kruppa

Eric Hahn wrote:
 
   If a person runs an ECM test using a B1 of 250,000 with 700
 curves (for up to 30 digits), will they also find any factors
 that they would have found if they had used a B1 of 50,000 with
 300 curves (for up to 25 digits) ?!?
 
 Eric

If the sigma is the same, then a curve with B1=25 will find any
factor that a curve with B1=5 finds.
When you run 700 random curves at B1=25, you might theoretically
miss a factor that someone else finds with B1=5, if he gets a lucky
sigma so that the group order is very smooth. But in general, using the
same number of curves, the higher bound should find all the factors that
the lower bound can find.
But dont be tempted into running only a few curves at very high bounds.
The strength of ECM is that you can try curves with different group
orders until a sufficiently smooth one comes along. So skipping bound
levels is usually not a good idea unless you have reason to believe the
the number unter attack has only large factors which call for a higher
bound.

Ciao,
  Alex.
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Re: Mersenne: GIMPS accelerator?

2001-05-16 Thread Alexander Kruppa

John R Pierce wrote:

 The newest Geforce3 chip also has both Pixel Shaders and Vertex Shaders
 which are each a SIMD programmable vector processors.  The Pixel Shaders
 operate on every pixel and generate the actual RGB pixels while the Vertex
 Processors operate on the geometry and texture mapping coordinates of the 3D
 mesh...   I don't know much about these, but pixels are only 8 bits per
 component so the pixel processors can't be very wide.

Could this help NFS sieving?

Ciao,
  Alex.
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Re: Mersenne: SUMOUT errors

2001-05-16 Thread Steve

For what it's worth, I have had the exact same problem getting illegal
sumouts when using the modem on this 475Mhz K6 PC. Hasn't happened since
january but had been happening about once a fortnight for months, and _only_
when the modem was heavily in use (Rockwell HCF 56K Data Fax PCI Modem). I
had forgotten all about it until I read Jeramy's message. It has never
happened on any of my other PCs. Oddly enough, I have noticed on Athlons
that the iterations run about 2% faster when the modem is connected!

Steve Harris

-Original Message-
From: Jeramy Ross
Date: Tuesday, May 15, 2001 9:24 PM
Subject: Re: Mersenne: SUMOUT errors


I don't really know how much help this will be since I don't know your
exact
situation and am not a expert by any means, but here goes!

First, the software modem may be a culprit.  I have had problems with ones
of the HSP variety.  Most show up as 'HSP Micromodem56' or something very
similar on your system.  Most of these modems also use a chipset
manufactured by PCTel.  Fairly stable, but use a nice chunk of CPU time
when
online, and I have received errors when I am checking email and/or surfing
the web while using this type of modem.  I have no hard evidence to tie
this
modem to the errors, but all errors happened when I was using that modem or
soon after (I hooked up a external modem just to see if the same would
happen with it and I did not receive errors when using it).  I have no idea
if you have a modem similar to that one or not, but it may be the problem.

Also, the electrical environment may be vastly different.  I am assuming
that where you had your computer was at school, and it is now at home.  At
my home, I have problems with various utility problems, and have been told
by others that utility problems could cause such errors.  I invested in a
UPS with line conditioning to hopefully control some of those problems.
Maybe one of these two things could be your problem.. I wish you the best
of
luck in finding and fixing the problem!

- Jeramy


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Mersenne: Newsgroup formation?

2001-05-16 Thread fay aron charles

 On Tue, May 15, 2001 at 10:23:33PM -, Brian J. Beesley wrote:
 If you understand _nothing_ discussed on a mailing list, there's no 
 point in subscribing. Similarly if you understand _everything_. You 
 can always delete the messages which you consider beyond your 
 intellect, or beneath contempt. Personally I like the range we have 
 at present.
 
 Yes -- that is my opinion too. I skim quite a lot, though ;-)

Personally, I really hate all mailing lists.  I was on one once where
somebody misused the system, and everybody (at once) complained by
emailing a complaint about the post to the base address.  Pretty soon
people started complaining about the complaints, saying the huge
traffic could be avoided if you had never complaind.  Before long,
someone thought it would be funny to send a 3MB attachment to everyone,
and soon others followed.

Now, I know the intellegence level here is __much__ higher, but I didn't
join for almost 2 years, because of my hatred of such groups.  I'm sure
this format is keeping many people away (especially the more experienced
netizens).

It seems a newsgroup is such a better medium for discussions like this.
Then, if I go on vacation for a month, I won't have to unsubscribe to
keep my INBOX from overflowing.  Also, a newsgroup will allow newbies
to read through old posts and see what types of question are asked.  This
is really the only way to keep the same questions from being asked over
and over.

But, most of all, I want threading.  If I have a K7 processor (I do),
I might not want to read about every bugfix in v.21, because it isn't
going to affect me.  The ability to skip threads is extremely powerful.

Oh, and did I mention that keeping my own archive of messages is really
eating my disk space?  Instead of 50 people saving the same message to
read later, it should just be kept on a newsgroup server, so that if 
I need to refer to it later, I just download it again. 

 -aron
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Re: Mersenne: Newsgruop formation?

2001-05-16 Thread Ryan M McGarry


I'm sure many of us on this mailing list are familiar with Slashdot, and
that the code behind it is open-source (known as Slashcode).  

For those of us who aren't, Slashdot (http://www.slashdot.org) is a news
website which covers news mainly in the interest of the Open Source
community.  About 10 of the latest news items are posted on the front
page, and each has a related discussion board automatically set up.

I propose that someone could implement and host our mailing list on this
website...  This could allow for people to browse through threads
easily, and allow people to catch up easily when joining for the first
time, or coming back from vacation.

The obvious problem to me is that the creation of new threads is
normally done manually, with only the most interesting/serious topics
being posted.  We won't be having hundreds of posts every day, but
somebody (or some group of us) will have to make sure that whenever
anybody requests a post, that it gets posted after meeting some
criteria...

In my opinion, the quality of some of the discussions on this mailing
list should be available to the public without having to subscribe to
the mailing list.  And this type of system will allow anonymous people
to post, maybe with valid points...

Just my two cents...

Ryan McGarry
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Re: Mersenne: Re: 26 exponents

2001-05-16 Thread Ken Kriesel

I believe that is set at the server.

Ken


At 08:25 AM 5/16/2001 +0100, Daran [EMAIL PROTECTED] wrote:
Does the client 'know' the threshold performance level for double-checks and
factorisations?  If so, is it hard-coded, or does it get this information
from
the server?  If hard-coded, then you have a problem with people continuing to
use older clients which tell them that it still makes 'most sense' to do
first-time checks, long after it has become more sensible to do double-checks
or factorisations.


Daran G.

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Re: QA (was re: Mersenne: Purpose of the self-test; also, aren't P4s fast!)

2001-05-16 Thread Ken Kriesel

At 10:56 AM 5/16/2001 -, Brian Beesley wrote:
On 16 May 2001, at 0:24, Ken Kriesel wrote:

 For the time being I would like to continue focussing our QA efforts on the
 general case, rather than P4's specific limits, since

Agreed. I was talking about the short test suite, where the runs 
stop after 400 iterations. We can generate the required data for a 
large number of exponents without diverting significant effort. In 
fact it's much easier to do this than it was a couple of years ago, 
as we have at least two reasonably efficient programs other than 
Prime95 which can be used to generate  cross-check the data.
 
 If I recall correctly, this does not require ridiculously small
exponents,
 since the convolution error falls off quickly away from our usual upper
 limit on exponent for a runlength. 

Quite correct. IMO it is ridiculous to run a whole LL test using a 
FFT run length of 2R when a run length of R would suffice; but 
running at least some 400-iteration short tests with a half size 
exponent during a self-test does make sense in two ways: it saves 
having to generate quite as much short run data (since we can recycle 
some of the smaller exponents into larger self-test run lengths), and 
- providing there is a temporary reduction in the rounding error 
limit whilst these short runs are in progress - we would be making 
the self-test more stringent.

Yes.  Even the next-longer runlength provides a very large drop in 
the expected convolution error for those exponents near the limit 
of a runlength.(orders of magnitude.)  Two to one on runlength is not needed.
The ratio 5:4 gives substantial reductions.

There is no point in optimizing the self-test for speed, since we are 
going to run the self-test for a fixed period of time.

There is some point in having the self-test resemble closely, actual running
conditions, to be as valid a test as possible, with respect to everything from
bit patterns to power loadings.



Ken

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Mersenne: Spacing between mersenne primes

2001-05-16 Thread Ken Kriesel

At 10:56 AM 5/16/2001 -, Brian J. Beesley [EMAIL PROTECTED] wrote:
Another point - we're coming up to the second anniversary of the 
discovery of M38(?) - I think we're overdue to find another one!

It would be nice to find another soon.  But I don't think we're overdue.

Long ago in Internet time I wrote:

Date: Thu, 29 Jan 1998 22:57:31 -0600
In mersenne primality testing, exponents double in magnitude are much 
more than double the work. For prime95 or the related versions,
each iteration takes about 2.1 times as long as an iteration for
half the FFT length, and there are twice as many iterations to perform,
per exponent.  The odds of a number being prime diminishes as the
magnitude increases.  Twice the FFT length is usable up to not quite twice
the exponent.

An interval of n to 2n contains nearly twice as many exponents as
the interval 1/2 n to n.  In either of these intervals we expect
based on experience, to find about the same number of mersenne primes
on the average.  (The actual rate of occurrence seems to be a little
bit in our favor for finding more primes in higher intervals, but it's
slight.)  That makes about 3 factors of 2.

I think to maintain a constant rate of discovery of new primes, we would
need to maintain about an 8 or 9-fold increase of computing resources per
period of exponent doubling.  Since exponent doubling has occurred in
about the past year, most of this must come in rapid growth in the cpu
pool, both by upgrades and by new membership.  Otherwise we can expect
to droop back to a lower discovery rate.  On average there are less than
2 mersenne primes per exponent doubling:
36 / [ln(2976221)/ln(2)] = 1.67 mersenne primes per doubling of exponent,
or about 37 / [ln(~300)/ln(2)] = 1.72 Mp's per doubling of p
(though we may have yet to find one in p  2976221, or slightly above!)

In the long run the present discovery rate is unsustainable.
Even if we do drop back to a discovery rate of one per two years,
from the recent ~2 per year, we will have moved this area ahead by
years from its old curve.  (The discovery rate was about 1 per 2 years 
over the past 20 year interval and for the past 40 year interval.)


Our experience described on http://www.mersenne.org/history.htm
bears this out.  And there is no particular reason to expect the time
interval, 
or the spacing between mersenne primes on a log or linear scale to be uniform.
It should vary about the expected curve.


Ken Kriesel

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Re: Mersenne: SUMOUT errors

2001-05-16 Thread Jeramy Ross

A interesting note, and I forgot to include this in my original post, but
the computer that I encountered the illegal sumouts on was a 500MHz K6 PC.
Perhaps this is a problem when running those software modems on a K6 based
machine??
- Jeramy

 Original Message - From: Steve [EMAIL PROTECTED]
 For what it's worth, I have had the exact same problem getting illegal
sumouts when using the modem on this 475Mhz K6 PC.

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Mersenne Digest V1 #853

2001-05-16 Thread Mersenne Digest


Mersenne DigestWednesday, May 16 2001Volume 01 : Number 853




--

Date: Tue, 15 May 2001 20:56:20 -0400 (EDT)
From: Jason Stratos Papadopoulos [EMAIL PROTECTED]
Subject: Re: Mersenne: GIMPS accelerator?

On Tue, 15 May 2001, Gareth Randall wrote:

 Also, any code would be very hardware specific, and may only work if
the display was not displaying, say, a desktop.
 
 However, if someone could implement it, it could provide the *ultimate*
in Mersenne related screen savers! What you'd see on the screen would be
the actual calculations themselves taking place before your eyes, and
with no overheads for displaying it either!


This question pops up every once in a while. A few years ago I looked
through a postscript manual wondering how difficult it would be to build a
postscript file that crunched RC5 keys when a printer tried to render it. 

The latest bleeding edge graphics cards are programmable to a limited
degree (am I thinking of the ATI Radeon here?) but not nearly programmable
enough, I'm sure. 

Heck, at least these ideas have a better chance than the guys who want to
crack the programming on kids' toys to make them crunch RC5 keys  :)

jasonp

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--

Date: Wed, 16 May 2001 01:32:15 + (GMT)
From: Russel Brooks [EMAIL PROTECTED]
Subject: Re: Mersenne: GIMPS accelerator?

John R Pierce wrote:
 Virtually all GPU's in use today are fixed function hard wired graphics
 accelerators.  There's no way to use them for general purpose computational
 use.   Also, there's no APIs, and each chip vendor has a radically different
 architecture.

Too bad, the idea might also have given us an interesting screen
saver as a side effect!  :-)

Cheers... Russ

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--

Date: Tue, 15 May 2001 20:58:34 -0500
From: Jeramy Ross [EMAIL PROTECTED]
Subject: Re: Mersenne: SUMOUT errors

I don't really know how much help this will be since I don't know your exact
situation and am not a expert by any means, but here goes!

First, the software modem may be a culprit.  I have had problems with ones
of the HSP variety.  Most show up as 'HSP Micromodem56' or something very
similar on your system.  Most of these modems also use a chipset
manufactured by PCTel.  Fairly stable, but use a nice chunk of CPU time when
online, and I have received errors when I am checking email and/or surfing
the web while using this type of modem.  I have no hard evidence to tie this
modem to the errors, but all errors happened when I was using that modem or
soon after (I hooked up a external modem just to see if the same would
happen with it and I did not receive errors when using it).  I have no idea
if you have a modem similar to that one or not, but it may be the problem.

Also, the electrical environment may be vastly different.  I am assuming
that where you had your computer was at school, and it is now at home.  At
my home, I have problems with various utility problems, and have been told
by others that utility problems could cause such errors.  I invested in a
UPS with line conditioning to hopefully control some of those problems.
Maybe one of these two things could be your problem.. I wish you the best of
luck in finding and fixing the problem!

- - Jeramy

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Date: Tue, 15 May 2001 19:21:08 -0700
From: John R Pierce [EMAIL PROTECTED]
Subject: Re: Mersenne: GIMPS accelerator?

 This question pops up every once in a while. A few years ago I looked
 through a postscript manual wondering how difficult it would be to build a
 postscript file that crunched RC5 keys when a printer tried to render it.

postscript is essentially forth, after all.  Trouble is, most postscript
interpreters are pretty damn slow.

 The latest bleeding edge graphics cards are programmable to a limited
 degree (am I thinking of the ATI Radeon here?) but not nearly programmable
 enough, I'm sure.

NVIDIA's chips are semi programmable too, but a big hurdle is lack of
documentation on the 3D rendering engine.  That stuff is trade secret.

I *do* suspect you could use the geometry engine (aka Transformation
Lighting and Projection) to do large numbers of fixed point 3x3
vector-matrix dot products with limited precision rather quickly.  The
question is, how useful would this be?  The pipeline is probably such that