Real zero in libpari

[Jeroen Demeyer <jdemeyer@cage.ugent.be>]

Hello pari-users,

I have a technical question about the t_REAL type.  The documentation
says that real zero is characterized by having the sign equal to zero.
My question is: does a real zero NEED to have lg == 2 in order to be a
valid GEN?

I am asking because the following program gives an error:
#include <pari/pari.h>
int main()
{
    pari_init(1000000, 500000);

    GEN x = cgetr(3);  /* Normally, lg would be 2 */
    setsigne(x, 0);
    setexpo(x, -63);
    dbgGEN(x, -1);

    /* The following line gives:
  ***   overflow in expo().
  ***   Error in the PARI system. End of program. */
    gexp(x, 100);
}


Cheers,
Jeroen.