#define NUM2PTR(x) ((SCM *) (SCM_UNPACK(x) & ~2))
{
  //C trampolines
  int ret; SCM *spp;
  const SCM *vec;
  int (*subr)(SCM **spp, int nargs, const SCM *closure, const SCM *end);


  
 vm_c_call:

  //printf("c call!\n");

  vec  = SCM_I_VECTOR_ELTS(SCM_CDR(program));

  
  //VM_HANDLE_INTERRUPTS;
  //SYNC_REGISTER ();
  
  spp  =  sp;
  SCM *sp_old = sp;
  //printf("dp %p\n",sp);
  subr = (subr_type) NUM2PTR(vec[0]);
  ret  = subr(&spp,nargs,vec + 1,stack_limit);

  //CACHE_REGISTER ();  

  sp   = spp;
  if(ret<0) 
    {
      //printf("return call\n");
      sp = sp + ret - 2;
      sp[0] = sp[-ret + 2];      
      //printf("dp %p, n = %d\n",(void *)(sp_old-sp), nargs);
      program = SCM_FRAME_PROGRAM (fp);
      NEXT;
    }

  nargs   = ret;
  program = sp[-nargs];
  
  if(SCM_CONSP(program) && scm_is_eq(SCM_CAR(program),c_closure_tag))
    goto vm_c_call;
  
  goto vm_call;

 vm_c_tail_call:
  vec = SCM_I_VECTOR_ELTS(SCM_CDR(program));
  subr    = (subr_type) NUM2PTR(vec[0]);

  //printf("c tail call!\n");
  
  //VM_HANDLE_INTERRUPTS;
  //SYNC_REGISTER ();
  

  spp = sp;
  ret = subr(&spp, nargs, vec + 1, stack_limit);

  //CACHE_REGISTER ();

  sp = spp;

  if(ret<0) 
    {
      sp = sp + ret + 1;
      goto vm_return;
    }

  nargs = ret;

  program = sp[-nargs];
  
  if(SCM_CONSP(program) && scm_is_eq(SCM_CAR(program),c_closure_tag))
    goto vm_c_tail_call;

  goto vm_tail_call;
}