On 07/29/2018 01:28 PM, Thomas Munro wrote:
> On Sun, Jul 29, 2018 at 10:57 PM, Thomas Munro
> <thomas.munro@enterprisedb.com> wrote:
>> On Sun, Jul 29, 2018 at 10:35 PM, Tomas Vondra
>> <tomas.vondra@2ndquadrant.com> wrote:
>>> It's always 0/-0 difference, and it's limited to power machines. I'll
>>> try to get access to such system and see what's wrong.
>>
>> This is suspicious:
>>
>> /* on some platforms, the preceding expression tends to produce -0 */
>> if (line->C == 0.0)
>> line->C = 0.0;
>
> I mean, it's suspiciously absent from the new line_construct()
> function. It was introduced here:
>
> commit 43fe90f66a0b200f6c32507428349afb45f661ca
> Author: Tom Lane <tgl@sss.pgh.pa.us>
> Date: Fri Oct 25 15:55:15 2013 -0400
>
> Suppress -0 in the C field of lines computed by line_construct_pts().
>
> It's not entirely clear why some PPC machines are generating -0 here, since
> the underlying computation should be exactly 0 - 0. Perhaps there's some
> wider-than-nominal-precision calculations happening? Anyway, the best way
> to avoid platform-dependent results seems to be to explicitly reset -0 to
> regular zero.
>
Hmm, I see. I think adding it to the else branch should do the trick,
then, I guess. But I'd be much happier if I could test it somewhere
before the commit.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
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