Re: Some bugs?

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

----- Original Message ----- 
From: "Jason Moxham" <jason@njkfrudils.plus.com>
To: <pari-dev@list.cr.yp.to>
Sent: Saturday, July 04, 2009 12:35 AM
Subject: Re: Some bugs?


> ----- 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


I've got a solution , although I'm not if this addresses the underlying 
cause.

In buch2.c there is a inline function called step if we rename this to 
step_buch2local and all the calls to it , then it works.

Why does this work?

There is another inline function called step in bibli1.c  , and it does't 
like two functions with the same name , they are both inlined , but perhaps 
the name scope is still global? , I'm getting a little out of my knowledge 
range here :)

I try a web search , see if I can come up with something.

Jason