presto-spi/src/main/java/io/prestosql/spi/type/UnscaledDecimal128Arithmetic.java/UnscaledDecimal128Arithmetic/subtract
class UnscaledDecimal128Arithmetic:    public static Slice subtract(Slice left, Slice right)
    {
        Slice result = unscaledDecimal();
        subtract(left, right, result);
        return result;
    }