Karim BELABAS on Thu, 21 Oct 1999 18:06:47 +0200 (MET DST)

 Re: removeprimes()

```[Igor:]
> I noticed this interesting behavior.
>
> 64
> 32
[...]
> So removeprimes() cuts the size of the list of
> declared primes in half.  I don't this this is how
> removeprimes() is described to behave.

Stupid bug (aren't they all :-). The argument to removeprimes() happens to be
the same (same pointer, not a copy) as the table we modify. This patch
special cases this situation (and cleans up the code while I was at it).

Karim.

Index: src/basemath/arith2.c
===================================================================
RCS file: /home/megrez/cvsroot/pari/src/basemath/arith2.c,v
retrieving revision 1.2
diff -c -r1.2 arith2.c
*** src/basemath/arith2.c	1999/10/15 11:30:40	1.2
--- src/basemath/arith2.c	1999/10/21 16:04:05
***************
*** 265,294 ****
avma=av; return primetab;
}

GEN
removeprimes(GEN prime)
{
!   long i,tx, av = avma;

if (!prime) return primetab;
tx = typ(prime);
if (is_vec_t(tx))
{
!     for (i=1; i < lg(prime); i++) removeprimes((GEN) prime[i]);
!     return primetab;
!   }
!   if (tx != t_INT) err(typeer,"removeprimes");
!   if (is_pm1(prime)) return primetab;
!   if (signe(prime) < 0) prime=absi(prime);
!
!   for (i=1; i < lg(primetab); i++)
!     if (egalii((GEN) primetab[i], prime))
{
!       gunclone((GEN)primetab[i]); primetab[i]=0;
!       cleanprimetab(); avma=av; return primetab;
}
!   err(talker,"prime is not in primetable in removeprimes");
!   return NULL; /* not reached */
}

/***********************************************************************/
--- 265,307 ----
avma=av; return primetab;
}

+ static GEN
+ removeprime(GEN prime)
+ {
+   long i;
+
+   if (typ(prime) != t_INT) err(typeer,"removeprime");
+   for (i=lg(primetab) - 1; i; i--)
+     if (absi_equal((GEN) primetab[i], prime))
+     {
+       gunclone((GEN)primetab[i]); primetab[i]=0;
+       cleanprimetab(); break;
+     }
+   if (!i) err(talker,"prime %Z is not in primetable", prime);
+   return primetab;
+ }
+
GEN
removeprimes(GEN prime)
{
!   long i,tx;

if (!prime) return primetab;
tx = typ(prime);
if (is_vec_t(tx))
{
!     if (prime == primetab)
{
!       for (i=1; i < lg(prime); i++) gunclone((GEN)prime[i]);
!       setlg(prime, 1);
}
!     else
!     {
!       for (i=1; i < lg(prime); i++) removeprime((GEN) prime[i]);
!     }
!     return primetab;
!   }
!   return removeprime(prime);
}

/***********************************************************************/
__
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
--