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Old 2005-08-15, 02:14   #1
sean
 
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Aug 2004
New Zealand

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Question segfault with large input on Opteron

$ echo '100000!-1' | ecm 1000
GMP-ECM 6.0.1 [powered by GMP 4.1.4] [ECM]
Input number is 100000!-1 (456574 digits)
Using B1=1000, B2=44623, polynomial x^1, sigma=1288196876
Step 1 took 3245570ms
Segmentation fault

I also tried running this with -v -v turned on. This produced a few lines with bignums on it. The last few lines before the segfault are:

B2'=65280 k=2 b2=32640 d=510 d2=1 dF=64, i0=1
Expected number of curves to find a factor of n digits:
20 25 30 35 40 45 50 55 60 65
3345 451878 1.1e+08 3.5e+10 inf inf inf inf inf inf
Initializing tables of differences for F took 86618ms
Computing roots of F took 320977ms

Any ideas?


The machine is a dual 1.8 GHz Opteron with 16GB of RAM.

Last fiddled with by sean on 2005-08-15 at 02:17 Reason: more info
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Old 2005-08-15, 07:55   #2
cjohnsto
 
Jun 2005

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Is GMP and ECM compiled using the stack or heap for number storage?
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Old 2005-08-15, 09:59   #3
akruppa
 
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Aug 2002
Alexandria

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After "Computing roots of F" it starts to build the polynomial F where arithmetic with large polynomials starts. The Kronecker-Schoenhage multiplication in GMP-ECM 6.0 uses a lot of temp space. As cjohnsto notes, the problem is probably that alloca() is used and it runs out of stack space.

Alex
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