presto-main/src/main/java/io/prestosql/type/VarcharOperators.java/VarcharOperators/hashCode
class VarcharOperators:    @LiteralParameters("x")
    @ScalarOperator(HASH_CODE)
    @SqlType(StandardTypes.BIGINT)
    public static long hashCode(@SqlType("varchar(x)") Slice value)
    {
        return xxHash64(value);
    }