presto-main/src/main/java/io/prestosql/operator/scalar/CombineHashFunction.java/CombineHashFunction/getHash
class CombineHashFunction:    @ScalarFunction(value = "combine_hash", hidden = true)
    @SqlType(StandardTypes.BIGINT)
    public static long getHash(@SqlType(StandardTypes.BIGINT) long previousHashValue, @SqlType(StandardTypes.BIGINT) long value)
    {
        return (31 * previousHashValue + value);
    }