  Ins_LOOPCALL( INS_ARG )
  {
    FT_ULong       F;
    TT_CallRec*    pCrec;
    TT_DefRecord*  def;


    /* first of all, check the index */
    F = args[1];
    if ( BOUNDS( F, CUR.maxFunc + 1 ) )
      goto Fail;

    /* Except for some old Apple fonts, all functions in a TrueType */
    /* font are defined in increasing order, starting from 0.  This */
    /* means that we normally have                                  */
    /*                                                              */
    /*    CUR.maxFunc+1 == CUR.numFDefs                             */
    /*    CUR.FDefs[n].opc == n for n in 0..CUR.maxFunc             */
    /*                                                              */
    /* If this isn't true, we need to look up the function table.   */

    def = CUR.FDefs + F;
    if ( CUR.maxFunc + 1 != CUR.numFDefs || def->opc != F )
    {
      /* look up the FDefs table */
      TT_DefRecord*  limit;


      def   = CUR.FDefs;
      limit = def + CUR.numFDefs;

      while ( def < limit && def->opc != F )
        def++;

      if ( def == limit )
        goto Fail;
    }

    /* check that the function is active */
    if ( !def->active )
      goto Fail;

    /* check stack */
    if ( CUR.callTop >= CUR.callSize )
    {
      CUR.error = TT_Err_Stack_Overflow;
      return;
    }

    if ( args[0] > 0 )
    {
      pCrec = CUR.callStack + CUR.callTop;

      pCrec->Caller_Range = CUR.curRange;
      pCrec->Caller_IP    = CUR.IP + 1;
      pCrec->Cur_Count    = (FT_Int)args[0];
      pCrec->Cur_Restart  = def->start;

      CUR.callTop++;

      INS_Goto_CodeRange( def->range, def->start );

      CUR.step_ins = FALSE;
    }
    return;

  Fail:
    CUR.error = TT_Err_Invalid_Reference;
  }

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.