Re: Some bugs?

["Jason Moxham" <jason@njkfrudils.plus.com>]

----- Original Message ----- 
From: "Bill Allombert" <Bill.Allombert@math.u-bordeaux1.fr>
To: <pari-dev@list.cr.yp.to>
Sent: Friday, July 03, 2009 11:41 PM
Subject: Re: Some bugs?


> On Fri, Jul 03, 2009 at 05:54:01PM +0100, Jason Moxham wrote:
> > ----- Original Message ----- From: "Bill Allombert"
> > <Bill.Allombert@math.u-bordeaux1.fr>
> > To: <pari-dev@list.cr.yp.to>
> > Sent: Friday, July 03, 2009 4:47 PM
> > Subject: Re: Some bugs?
> >
> >
> > and here is parisvn with MSVC32 no GMP
> > break> bnfinit(x^2+105)
> > Time disc. factorisation: 0
> > Treating p^k = 2^2
> > Time round4: 0
> > get_red_G: starting LLL, prec = 4 (4 + 0)
> > Time LLL basis: 0
> > Time mult. table: 0
> > Time matrices: 0
> > Time nfinit & rootsof1: 0
> > R1 = 0, R2 = 1
> > D = 420
> > LIMC = 20, LIMC2 = 20
> > Time factor base: 0
> > Time sub factorbase (3 elements): 0
> > KCZ = 7, KC = 10, n = 15
> > 1 2 3 4 5 6 7
> > #### Looking for 15 relations (small norms)
> >  ***   at top-level: bnfinit(x^2+105)
> >  ***                 ^----------------
> >  *** bnfinit: bug in PARI/GP (Segmentation Fault), please report
> >  ***   Break loop: type <Return> three times, or Control-d, to go back to
> > GP)
>
> So this is a problem with the function small_norm.
> Maybe you could use debugger to pin-point it ?
> (there is a definite possibility that small_norm has a bug which does
> manifest itself on Linux).
>
> Cheers,
> Bill.


I don't know how to use the windows CL debugger  , so doing it the old 
fashioned way.
in buch2.c from line 2120 we have

   BOUND *= 1 + 1e-6;
   k = N; y[N] = z[N] = 0; x[N] = 0;
   for (av2 = avma;; avma = av2, step(x,y,inc,k))            // POSITION 1
   {                                                                        
        // POSITION 5
     do
     { /* look for primitive element of small norm, cf minim00 */
       int fl = 0;
       double p;
       if (k > 1)
       {
         long l = k-1;
         z[l] = 0;
         for (j=k; j<=N; j++) z[l] += q[l][j]*x[j];
         p = (double)x[k] + z[k];
         y[l] = y[k] + p*p*v[k];
         if (l <= skipfirst && !y[1]) fl = 1;
         x[l] = (long)floor(-z[l] + 0.5);
         k = l;
       }
       for(;; step(x,y,inc,k))
       {
         if (!fl)
         {
           p = (double)x[k] + z[k];
           if (y[k] + p*p*v[k] <= BOUND) break;

           step(x,y,inc,k);

           p = (double)x[k] + z[k];
           if (y[k] + p*p*v[k] <= BOUND) break;
         }
         fl = 0; inc[k] = 1;
         if (++k > N) goto ENDIDEAL;
       }
     } while (k > 1);

     /* element complete */                    //        POSITION 2
     if (zv_content(x) !=1) continue; /* not primitive */     // POSITION 3
     gx = ZM_zc_mul(IDEAL,x);                // POSITION 4
     if (ZV_isscalar(gx)) continue;


the code goes thru pos 1 thru to pos 2 then 3 does not go to 4 but goes 
back to 1 , it never gets to pos 5
there is no exit condition on the for loop so it must crash in 
step(x,y,inc,k)  , whether this the cause , I dont know ?

I'll keep looking
Jason