Re: bug report

[Karim BELABAS <Karim.Belabas@math.u-psud.fr>]

[Cliff Bergman:]
> Hello.  I just (twice) got an error starting from a clean invocation of gp
> 2.0.17 (under Redhat Linux 6.1) after the following computations:
> 
> ? ec=[0,0,0,-Mod(1,13),-Mod(3,13)]
> %1 = [0, 0, 0, Mod(12, 13), Mod(10, 13)]
> ? c=ellinit(ec,1)
> %2 = [0, 0, 0, Mod(12, 13), Mod(10, 13), 0, Mod(11, 13), Mod(1, 13), Mod(12, 13), Mod(9, 13), Mod(5, 13), Mod(11, 13), Mod(6, 13)]
> ? c.disc
> %3 = Mod(11, 13)
> ? c.roots
>   ***   segmentation fault: bug in GP (please report).
> 
> I'm just doing as requested: reporting the error.  Enjoy!

Hi,

  as Gerhard Niklasch already mentioned on pari-dev, this is simply a matter
of an expected component not being there (and the member function forgetting
to check about it...). I corrected the problem on the CVS version a few
minutes ago:

(17:49) gp > c.roots
  ***   incorrect type in .roots: c.roots
                                    ^-----

I double checked all member functions and found a number of other examples
where "random" input could wreak havoc (but you found the simplest one, by
far!). I tried to make sure segmentation faults are always avoided when a
structure component is requested, whatever the input [ This is easy and cheap
whereas the corresponding behaviour is currently unattainable for library
mode functions, given PARI's (very weak) notion of "type checking" ].

Cheers,

   Karim.
__
Karim Belabas                    email: Karim.Belabas@math.u-psud.fr
Dep. de Mathematiques, Bat. 425
Universite Paris-Sud             Tel: (00 33) 1 69 15 57 48
F-91405 Orsay (France)           Fax: (00 33) 1 69 15 60 19
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PARI/GP Home Page: http://www.parigp-home.de/