instance_of?

VALUE
rb_obj_is_instance_of(VALUE obj, VALUE c)
{
    switch (TYPE(c)) {
      case T_MODULE:
      case T_CLASS:
      case T_ICLASS:
        break;
      default:
        rb_raise(rb_eTypeError, "class or module required");
    }

    if (rb_obj_class(obj) == c) return Qtrue;
    return Qfalse;
}