| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | emre(at)hasegeli(dot)com |
| Cc: | Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: line_perp() (?-|) is broken. |
| Date: | 2018-03-03 15:43:26 |
| Message-ID: | 31399.1520091806@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Emre Hasegeli <emre(at)hasegeli(dot)com> writes:
>> Possibly this objection is pointless, because I'm not at all sure that
>> the existing code is careful about how it uses FPeq/FPzero; perhaps
>> we're applying EPSILON to all manner of numbers that don't have units
>> of the coordinate space. But this won't help make it better.
> The existing code was probably paying attention to this particular
> one, but it fails to apply EPSILON meaningfully to many other places.
> For example lseg_parallel() and lseg_perp() applies it 2 times to the
> same input. First point_sl() compares x coordinates with FPeq(), and
> then the returned slopes are compared again with FPeq().
Yeah, comparing a slope to EPSILON sure feels wrong :-(
regards, tom lane
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