At 10:01 AM 1999/03/02 -0500, Paul Derbyshire <[EMAIL PROTECTED]> wrote:
>At 02:01 PM 2/28/99 -0500, you wrote:
>>Finding an error in the first LL test is not rare. I've said about 1 in
>>200 are incorrect.
>
>Yeah, but most of those are "silent mutations" in nonzero residues, not
>errors in the purported primality result, right?
Right. The odds heavily favor both mismatched residues being nonzero.
A zero residue at the last iteration is what indicates primality.
>Also what causes the errors, bugs in the code?
What I've seen most often is that prime95 and its relatives provide
early warning of unreliable hardware, whether cpu, RAM module, or motherboard.
>Is work being done on
>finding subtle errors in the software?
Yes, in the sense that for the first two+ years, double checking was done
only on a different program on a different processor architecture than the
original check, and currently some double checks do so still. Either
programming errors or chip design errors would surface in that scenario.
I've volunteered to run on Intel, one or two exponents in each run length
to try out the code before the bulk of the GIMPS effort is routinely being
assigned exponents in the higher run lengths. Perhaps someone running a
different architecture would be willing to double check them.
George has made provisions both to detect some errors and to prevent those
from causing the loss of all work up to that point on the exponent.
For example:
Iteration: 3743629/5070277, ERROR: SUM(INPUTS) != SUM(OUTPUTS),
5.26887446743531e+016 != 1.990777258736701e+016
Possible hardware failure, consult the readme file.
Continuing from last save file.
means an error has occurred and been detected, and to save the last few
weeks' work, the last half hours' is discarded and tried again.
>Are some of them, in the case of
>Prime95, caused by Winblows?
Iteration: 1407235/5070277, ERROR: ILLEGAL SUMOUT
Possible hardware failure, consult the readme file.
Continuing from last save file.
Possibly these are software, according to George's readme.txt, under the
section Possible Hardware Failure
If it is software, it is not necessarily the fault of Windows or Microsoft.
Could be a bum driver not doing things it should.
>(IOW, are there more errors per P90 CPU hour
>among Winblows boxes than among mprime boxes?)
>
>I figure only a small percentage of participants have actual faulty
>hardware, and that spurious cosmic ray bit flips are caught by checksumming
>of some kind. (Is that what ILLEGAL SUMOUT is, a checksum mismatch?)
________________________________________________________________
Unsubscribe & list info -- http://www.scruz.net/~luke/signup.htm
