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Old 2016-02-02, 15:13   #1
mattmill30
 
Aug 2015

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Default mfaktc: Mis-reported composite factor

Further to http://www.mersenneforum.org/showthread.php?t=20943, I understand that during a T77-81, using the 95bit_mul32_gs kernel, corruption went undetected.

Apparently mfaktc switched both the exponent and bitlevel being analysed.

I've repeated the test without the same factor being reported.
Note: The original factor result was still in results.txt during the retest.

The main change I can think of between the two tests, is the random intervals at which the tests were stopped to improve graphics responsiveness for whilst the computer was in use.

I believe mfaktc was configured for both tests with:
SievePrimes=200000
NumStreams=1
GridSize=3
Stages=0
StopAfterFactor=0
SieveOnGPU=1
GPUSievePrimes=1075000
GPUSieveSize=128
GPUSieveProcessSize=32

Since the factor is 95bits in length, is there a memory bug in the 95bit_mul32 kernel?
Also, the factor is returned as part of the self test, so does the kernel have bug which caused it to initiate and report on a self-test?
(http://www.mersenneforum.org/showpos...postcount=1123)
Note: Though the TF run would have been continuation from a checkpoint, I'm not certain whether the result was reported before (self-test), during (M332347303) or on termination (CTRL+C).

Why would mfaktc choose 95bit_mul32_gs over barrett87_mul32_gs for factoring T77-81?
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Old 2016-02-05, 19:41   #2
TheJudger
 
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"Oliver"
Mar 2005
Germany

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Quote:
Originally Posted by mattmill30 View Post
Why would mfaktc choose 95bit_mul32_gs over barrett87_mul32_gs for factoring T77-81?
Because you set "Stages=0". The barett92/88/87 family can only do a single bitlevel at once.
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