// static void  PerlPower(int a, int b)
static void callback()
 {
   dSP;                            /* initialize stack pointer      */
   ENTER;                          /* everything created after here */
   SAVETMPS;                       /* ...is a temporary variable.   */
   PUSHMARK(SP);                   /* remember the stack pointer    */
   XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack  */
   XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack  */
   PUTBACK;                      /* make local stack pointer global */
//   call_pv("expo", G_SCALAR|G_DISCARD|G_NOARGS);      /* call the function             */

   call_pv("p_callback", G_DISCARD|G_NOARGS);

   SPAGAIN;                        /* refresh stack pointer         */
                                 /* pop the return value from stack */
//   printf ("%d to the %dth power is %d.\n", a, b, POPi);
   PUTBACK;
   FREETMPS;                       /* free that return value        */
   LEAVE;                       /* ...and the XPUSHed "mortal" args.*/
 }