Re: Comparing two double values method
Heikki Linnakangas 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
Re: Comparing two double values method
You're right, I made a mistake. Thanks for your explanation.
Re: Comparing two double values method
On 10/10/2023 13:31, Bowen Shi wrote: Dears, I noticed that in the `check_GUC_init` function, there is a direct comparison using the != operator for two double values, which seems problematic. I wrote this patch to fix this. No, the compile-time initial values should match exactly. -- Heikki Linnakangas Neon (https://neon.tech)
Re: Comparing two double values method
On Tue, 10 Oct 2023 at 12:33, Bowen Shi wrote: > > Dears, > > I noticed that in the `check_GUC_init` function, there is a direct > comparison using the != operator for two double values, which seems > problematic. I don't think I understand the problem. The code checks that the dynamic initialization values are equal to the current value of the GUC, or 0. Why would a "margin for error" of 1e-6 be of any use? Why was the margin of 1e-6 chosen instead of one based on the exponent of the GUC's current value (if any)? In my view, this would break the code, not fix it, as it would decrease the cases where we detect broken GUC registrations. Kind regards, Matthias van de Meent Neon (https://neon.tech)
Comparing two double values method
Dears, I noticed that in the `check_GUC_init` function, there is a direct comparison using the != operator for two double values, which seems problematic. I wrote this patch to fix this. -- Regard, Bowen Shi v1-0001-Fix-double-value-compare-problem.patch Description: Binary data
