==

static VALUE
exc_equal(VALUE exc, VALUE obj)
{
    VALUE mesg, backtrace;
    const ID id_mesg = idMesg;

    if (exc == obj) return Qtrue;

    if (rb_obj_class(exc) != rb_obj_class(obj)) {
        int status = 0;
        ID id_message, id_backtrace;
        CONST_ID(id_message, "message");
        CONST_ID(id_backtrace, "backtrace");

        obj = rb_protect(try_convert_to_exception, obj, &status);
        if (status || obj == Qundef) {
            rb_set_errinfo(Qnil);
            return Qfalse;
        }
        if (rb_obj_class(exc) != rb_obj_class(obj)) return Qfalse;
        mesg = rb_check_funcall(obj, id_message, 0, 0);
        if (mesg == Qundef) return Qfalse;
        backtrace = rb_check_funcall(obj, id_backtrace, 0, 0);
        if (backtrace == Qundef) return Qfalse;
    }
    else {
        mesg = rb_attr_get(obj, id_mesg);
        backtrace = exc_backtrace(obj);
    }

    if (!rb_equal(rb_attr_get(exc, id_mesg), mesg))
        return Qfalse;
    if (!rb_equal(exc_backtrace(exc), backtrace))
        return Qfalse;
    return Qtrue;
}