Re: Comparing two double values method

Heikki Linnakangas <hlinnaka(at)iki(dot)fi> writes:
> On 10/10/2023 13:31, Bowen Shi wrote:
>> I noticed that in the `check_GUC_init` function, there is a direct
>> comparison using the != operator for two double values, which seems
>> problematic.

> No, the compile-time initial values should match exactly.

Right. The point of this test is to catch cases where you wrote,
say,

double my_guc = 1.1;

but the boot_val for it in guc_tables.c is 1.2. There is no
reason to allow any divergence in the spellings of the two C
literals, so as long as they're compiled by the same compiler
there's no reason to expect that the compiled values wouldn't
be bit-equal.

The point of the exclusions for zero is to allow you to just
write

double my_guc;

without expressing an opinion about the initial value.
(Yes, this does mean that "double my_guc = 0.0;" could
be misleading. It's just a heuristic though.)

regards, tom lane