presto-spi/src/main/java/io/prestosql/spi/type/UnscaledDecimal128Arithmetic.java/UnscaledDecimal128Arithmetic/isNegative
class UnscaledDecimal128Arithmetic:    public static boolean isNegative(long rawLow, long rawHigh)
    {
        return (rawHigh & SIGN_LONG_MASK) != 0;
    }