| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Vik Fearing <vik(dot)fearing(at)2ndquadrant(dot)com> |
| Cc: | Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, Stephen Frost <sfrost(at)snowman(dot)net>, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>, Chapman Flack <chap(at)anastigmatix(dot)net>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Greatest Common Divisor |
| Date: | 2020-01-04 00:34:04 |
| Message-ID: | 15876.1578098044@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Vik Fearing <vik(dot)fearing(at)2ndquadrant(dot)com> writes:
> On 04/01/2020 01:21, Tom Lane wrote:
>> Zero is the "correct" answer for that, isn't it, independently of overflow
>> considerations?
> I would say not.
Oh, right, I was misremembering the identity gcd(a,0) as being 0 not a.
Never mind that then.
> The correct answer is INT_MIN but we've decided a
> negative result is not desirable.
Agreed. On the other hand, we could stave off overflow the same
way we discussed for lcm: make it return int8. We're still stuck
with the special case for INT64_MIN in gcd64 of course, so maybe
that's just inconsistent rather than being worthwhile.
[ thinks for a bit... ] In practice, I imagine few people use gcd on
negative values, so doing weird things with the datatype choices is
probably not better than throwing an error for this case.
regards, tom lane
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