Method do_check

sql/sys_vars.h:141–246

    DBUG_ASSERT(def_val % block_size == 0);
  }
  bool do_check(THD *thd, set_var *var)
  {
    my_bool fixed= FALSE;
    longlong v;
    ulonglong uv;
    const T *vmin, *vmax;

    v= var->value->val_int();
    if (SIGNED) /* target variable has signed type */
    {
      if (var->value->unsigned_flag)
      {
        /*
          Input value is such a large positive number that MySQL used an
          unsigned item to hold it. When cast to a signed longlong, if the
          result is negative there is "cycling" and this is incorrect (large
          positive input value should not end up as a large negative value in
          the session signed variable to be set); instead, we need to pick the
          allowed number closest to the positive input value, i.e. pick the
          biggest allowed positive integer.
        */
        if (v < 0)
          uv= max_of_int_range(ARGT);
        else /* no cycling, longlong can hold true value */
          uv= (ulonglong) v;
      }
      else
        uv= v;
      /* This will further restrict with VALID_RANGE, BLOCK_SIZE */
      var->save_result.ulonglong_value=
        getopt_ll_limit_value(uv, &option, &fixed);
    }
    else
    {
      if (var->value->unsigned_flag)
      {
        /* Guaranteed positive input value, ulonglong can hold it */
        uv= (ulonglong) v;
      }
      else
      {
        /*
          Maybe negative input value; in this case, cast to ulonglong makes it
          positive, which is wrong. Pick the closest allowed value i.e. 0.
        */
        uv= (ulonglong) (v < 0 ? 0 : v);
      }
      var->save_result.ulonglong_value=
        getopt_ull_limit_value(uv, &option, &fixed);
    }

    if (max_var_ptr())
    {
      /* check constraint set with --maximum-...=X */
      if (SIGNED)
      {
        longlong max_val= *max_var_ptr();
        if (((longlong)(var->save_result.ulonglong_value)) > max_val)