BUG #19586: money division overflow

The following bug has been logged on the website:

Bug reference: 19586
Logged by: Michael Malis
Email address: malis@pgrust.com
PostgreSQL version: 18.4
Operating system: Linux x86_64 and Linux aarch64
Description:

cash_div_int64() in src/backend/utils/adt/cash.c guards against division by
zero but not against the INT64_MIN / -1 overflow:

cash_div_int64(Cash c, int64 i)
{
if (unlikely(i == 0))
ereport(ERROR, (errcode(ERRCODE_DIVISION_BY_ZERO), ...));
return c / i;
}

Commit 4f96281587 ("Add overflow checks to money type", 2024-07-19, fixing
bug
#18240) added pg_mul_s64_overflow() checks to cash_mul_int64() and the
float paths, but the division path was not covered.

Steps to reproduce

SELECT '-92233720368547758.08'::money / -1;

Actual results

On x86-64, the hardware division trap is caught by PostgreSQL's SIGFPE
handler and surfaces as a misleading error class for an integer overflow:

ERROR: floating-point exception
DETAIL: An invalid floating-point operation was signaled...
On aarch64, where the division does not trap, the wrong value is returned
silently, with no error:

-$92,233,720,368,547,758.08
i.e. a negative value divided by -1 remains negative.

Expected results

The same treatment int8div() already gives the identical arithmetic, on
every platform:

SELECT (-9223372036854775808)::bigint / -1;
ERROR: bigint out of range

Multiplication in the money type is already guarded and behaves correctly:

SELECT '-92233720368547758.08'::money * -1;
ERROR: money out of range

I would be happy to provide a patch.