// Special case handling for NaN. NaN is equal to NaN but
// otherwise always compares to false.
if (std::isnan(e.numberDouble()) || std::isnan(_rhs.numberDouble())) {
    bool bothNaN = std::isnan(e.numberDouble()) && std::isnan(_rhs.numberDouble());
    switch ( matchType() ) {
    case LT:
        return false;
    case LTE:
        return bothNaN;
    case EQ:
        return bothNaN;
    case GT:
        return false;
    case GTE:
        return bothNaN;
    default:
        // This is a comparison match expression, so it must be either
        // a $lt, $lte, $gt, $gte, or equality expression.
        fassertFailed( 17448 );
    }
}