Re: [PATCH] Add tests for Bitmapset

On Sep 16 2025, at 8:35 pm, Michael Paquier <michael(at)paquier(dot)xyz> wrote:

> On Tue, Sep 16, 2025 at 03:00:40PM -0700, Masahiko Sawada wrote:
>> Thank you for updating the patch. It seems cfbot caught a regression
>> test error[1] in a 32-bit build.
>
> - bitmap_hash [1,3,5] | 49870778
> + bitmap_hash [1,3,5] | 1509752520
>
> This one is able the hash value computation being not portable across
> architectures. I would just change these to be non-NULL, I guess.
> --
> Michael

Thanks Michael, Sawada-san, yep hashing is arch dependent (go figure!),
but thankfully it is deterministic. Rather that test for non-NULL I've
come up with this approach:

-- Architecture-aware hash testing
WITH arch_info AS (
SELECT
CASE
WHEN pg_column_size(1::bigint) = 8 THEN '64bit'
ELSE '32bit'
END as architecture
),
expected_values AS (
SELECT
architecture,
CASE architecture
WHEN '64bit' THEN 0
WHEN '32bit' THEN 0
END as hash_null,
CASE architecture
WHEN '64bit' THEN 49870778
WHEN '32bit' THEN 1509752520
END as hash_135,
CASE architecture
WHEN '64bit' THEN -303921606
WHEN '32bit' THEN 0 -- TBD
END as hash_246
FROM arch_info
)
SELECT 'expected hash NULL' as test,
test_bitmap_hash(NULL) = hash_null as result
FROM expected_values
UNION ALL
SELECT 'expected hash [1,3,5]' as test,
test_bitmap_hash(test_bms_from_array(ARRAY[1,3,5])) = hash_135 as result
FROM expected_values
UNION ALL
SELECT 'expected hash [2,4,6]' as test,
test_bitmap_hash(test_bms_from_array(ARRAY[2,4,6])) = hash_246 as result
FROM expected_values;

However I'm not sure what the value is for testing hash functions except
for coverage and I'm fairly certain that function is well exercised.
That said, I think that will work. I'll let cfbot tell me the 32bit
hash value on the next run.

thanks again for the helpful insights,

-greg