presto-spi/src/main/java/io/prestosql/spi/type/UnscaledDecimal128Arithmetic.java/UnscaledDecimal128Arithmetic/setNegativeLong
class UnscaledDecimal128Arithmetic:    private static void setNegativeLong(Slice decimal, long high, boolean negative)
    {
        setRawLong(decimal, SIGN_LONG_INDEX, high | (negative ? SIGN_LONG_MASK : 0));
    }