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Old 2016-11-12, 17:33   #1
Romuald
 
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Oct 2015
France

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Default Seg fault with various programs

Hi,

I've noticed that for a certain amount of mersenne numbers, in some programs, in principle not related between them, a segmentation fault occurs.
Here are some examples in YAFU and PARI/GP:

Code:
>> factor(2^273-1)

fac: factoring 15177100720513508366558296147058741458143803430094840009779784451085189728165691391
fac: using pretesting plan: normal
fac: no tune info: using qs/gnfs crossover of 95 digits

starting SIQS on c36: 356017128048164475524315650309423081

==== sieving in progress ( 4 threads):     448 relations needed ====
====            Press ctrl-c to abort and save state            ====
Erreur de segmentation (core dumped)003 partial, (37494.25 rels/sec)
Code:
factorint(2^273-1)
IFAC: cracking composite
  
... (a lot of lines)

MPQS: starting Gauss over F_2 on 722 relations
  ***   at top-level: factorint(2^273-1)
  ***                 ^------------------
  *** factorint: bug in PARI/GP (Segmentation Fault), please report.
  ***   Break loop: type 'break' to go back to GP prompt
Any idea why this often occurs? How to fix it? As far as I know, it seems to be a known common issue.

Last fiddled with by Romuald on 2016-11-12 at 17:34
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Old 2016-11-13, 11:18   #2
bgbeuning
 
Dec 2014

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My first guess would be unstable hardware.
Try prime95 in torture test mode.
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Old 2016-11-13, 14:29   #3
Romuald
 
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I will. I only find this strange. I don't see why my hardware would be so unstable.
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Old 2016-11-14, 05:38   #4
LaurV
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Jun 2011
Thailand

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My money is on bad memory.

There is nothing to "stress" the hardware (CPU. etc) there, 2^273-1 is a ~200-300 ms job, your CPU could be able to do it even without a cooler.

edit:

Code:
gp > factor(2^273-1)
time = 345 ms.
%1 =
[                   7 2]
[                  79 1]
[                 127 1]
[                 337 1]
[                 911 1]
[                8191 1]
[              121369 1]
[           108749551 1]
[           112901153 1]
[         23140471537 1]
[    4093204977277417 1]
[86977595801949844993 1]

gp > factorint(2^273-1)
time = 141 ms.
%2 =
[                   7 2]
[                  79 1]
[                 127 1]
[                 337 1]
[                 911 1]
[                8191 1]
[              121369 1]
[           108749551 1]
[           112901153 1]
[         23140471537 1]
[    4093204977277417 1]
[86977595801949844993 1]
Code:
===============================================================
======= Welcome to YAFU (Yet Another Factoring Utility) =======
=======             bbuhrow@gmail.com                   =======
=======     Type help at any time, or quit to quit      =======
===============================================================
cached 78498 primes. pmax = 999983

>> factor(2^273-1)
fac: factoring 15177100720513508366558296147058741458143803430094840009779784451085189728165691391
fac: using pretesting plan: custom
fac: custom pretest ratio is: 0.3300
fac: no tune info: using qs/gnfs crossover of 95 digits
div: primes less than 10000
rho: x^2 + 3, starting 1000 iterations on C68
rho: x^2 + 2, starting 1000 iterations on C68
rho: x^2 + 2, starting 1000 iterations on C63
rho: x^2 + 1, starting 1000 iterations on C63
pm1: starting B1 = 150K, B2 = gmp-ecm default on C63
ecm: 30/30 curves on C36, B1=2K, B2=gmp-ecm default

starting SIQS on c36: 356017128048164475524315650309423081

==== sieving in progress (1 thread):     432 relations needed ====
====           Press ctrl-c to abort and save state           ====
408 rels found: 213 full + 195 from 1692 partial, (11656.79 rels/sec)

SIQS elapsed time = 0.1965 seconds.

fac: factoring 284117545476067356557759711
fac: using pretesting plan: normal
fac: no tune info: using qs/gnfs crossover of 95 digits
div: primes less than 10000
fmt: 1000000 iterations
rho: x^2 + 3, starting 1000 iterations on C27
rho: x^2 + 2, starting 1000 iterations on C27
rho: x^2 + 1, starting 1000 iterations on C27
pm1: starting B1 = 150K, B2 = gmp-ecm default on C27
ecm: 0/30 curves on C27, B1=2K, B2=gmp-ecm default
ecm: 0/29 curves on C19, B1=2K, B2=gmp-ecm default

Total factoring time = 0.2607 seconds
Total factoring time = 1.5470 seconds

***factors found***

P1 = 7
P1 = 7
P2 = 79
P3 = 127
P3 = 337
P3 = 911
P4 = 8191
P6 = 121369
P20 = 86977595801949844993
P16 = 4093204977277417
P9 = 108749551
P11 = 23140471537
P9 = 112901153

Last fiddled with by LaurV on 2016-11-14 at 05:47
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