Bill Allombert on Wed, 03 Feb 2010 21:42:58 +0100

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Re: ellap hangs on a large-ish prime

On Tue, Feb 02, 2010 at 01:56:42PM +0100, Andreas Enge wrote:
> On Tue, Feb 02, 2010 at 01:05:06PM +0100, Bill Allombert wrote:
> > Precisely: Version 2.4.3 include an implementation of SEA which run
> > polynomial time, however for a small prime like 2486152157 it still
> > use the older algorithm, so this is unrelated.
> In any case, the problem seems to be solved in the current svn.
> The original poster's gp script
> E = ellinit([0,0,1,-1,0]);
> P = 2486152157;
> ellap(E, P)
> returns -13740 in no time.

I am not sure the issue is properly addressed in the current SVN:
I do not see what prevent points from having 0 coordinates passed
to mod2BIL. The function _fix() use lgefint where lg should be
used, and I found a case where ellap1 return p+ap (bug #1030), so
this bug might still exist in SVN.

Probably this thread should be moved to pari-dev now.