Re: [PATCH] Improve geometric types

On Sun, Jul 29, 2018 at 10:57 PM, Thomas Munro
<thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> On Sun, Jul 29, 2018 at 10:35 PM, Tomas Vondra
> <tomas(dot)vondra(at)2ndquadrant(dot)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(at)sss(dot)pgh(dot)pa(dot)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.

--
Thomas Munro
http://www.enterprisedb.com