Re: [PATCH] Improve geometric types

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.

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