presto-main/src/main/java/io/prestosql/type/CharOperators.java/CharOperators/hashCode
class CharOperators:    @LiteralParameters("x")
    @ScalarOperator(HASH_CODE)
    @SqlType(StandardTypes.BIGINT)
    public static long hashCode(@SqlType("char(x)") Slice value)
    {
        return XxHash64.hash(value);
    }