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Old 2008-02-16, 23:18   #1
D. B. Staple
 
D. B. Staple's Avatar
 
Nov 2007
Halifax, Nova Scotia

23×7 Posts
Default Bug with ECM on mprime

Hello all,

I seem to be running into a bug when using mprime 24.14.2 to perform ECM on the Fermat number F20. Specifically the bug is that mprime falsely reports having found a factor, and yet the reported factor is the number F20 itself (all 300000+ digits of it). This is very discouraging as I am trying to perform a major attack on this number, but now I don't know if any of my results can be trusted.

I have tried rerunning one of the jobs with the same parameters and seed but it seems that the errors are not reproducible. On the other hand the error has occurred more than once on different curves (six out of roughly 100 curves have failed this way). Note that this was on a cluster of computers so I am therefore not certain if this is some sort of hardware error on my end or a legitimate software bug. I do not want to compromise the search for factors of Fermat numbers by reporting erroneous negative results, on the other hand I would rather not waste the processor time which I have already used by not reporting it (roughly 2 cpu years). My question is simply whether or not I should trust the results of my computations, i.e., that no factors have been found in the curves which did not produce errors.

If you are interested in the details of the hardware/software being used, I have appended the info contained in /proc/cpuinfo, meminfo, and version. Let me know if you would like further details of the conditions under which the bug occurred.

Thanks again,

Doug



Linux version 2.4.20-28.8smp (bhcompile@daffy.perf.redhat.com) (gcc version 3.2 20020903 (Red Hat Linux 8.0 3.2-7)) #1 SMP Thu Dec 18 12:25:21 EST 2003

processor : 0
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.80GHz
stepping : 7
cpu MHz : 2790.898
cache size : 512 KB
Physical processor ID : -1069960964
Number of siblings : 1
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
bogomips : 5539.46

processor : 1
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.80GHz
stepping : 7
cpu MHz : 2790.898
cache size : 512 KB
Physical processor ID : -1069960956
Number of siblings : 1
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
bogomips : 5573.87

total: used: free: shared: buffers: cached:
Mem: 2114199552 885940224 1228259328 0 251641856 575942656
Swap: 4293541888 13045760 4280496128
MemTotal: 2064648 kB
MemFree: 1199472 kB
MemShared: 0 kB
Buffers: 245744 kB
Cached: 558200 kB
SwapCached: 4244 kB
Active: 425148 kB
Inact_dirty: 338804 kB
Inact_clean: 53236 kB
Inact_target: 163436 kB
HighTotal: 1179584 kB
HighFree: 603896 kB
LowTotal: 885064 kB
LowFree: 595576 kB
SwapTotal: 4192912 kB
SwapFree: 4180172 kB
Committed_AS: 38896 kB
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