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