Re: Greatest Common Divisor

From: Vik Fearing <vik(dot)fearing(at)2ndquadrant(dot)com>
To: Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
Cc: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Stephen Frost <sfrost(at)snowman(dot)net>, 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 21:31:43
Message-ID: 535e8b2f-325b-788a-9dd9-58b170f45f98@2ndquadrant.com
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-hackers

On 04/01/2020 20:08, Dean Rasheed wrote:
> On Sat, 4 Jan 2020 at 17:55, Vik Fearing <vik(dot)fearing(at)2ndquadrant(dot)com> wrote:
>> On 04/01/2020 10:37, Dean Rasheed wrote:
>>> BTW, there is actually no need to restrict the inputs to integral
>>> values because GCD is something that has a perfectly natural extension
>>> to floating point inputs (see for example [1]). Moreover, since we
>>> already have a mod(numeric, numeric) that works for arbitrary inputs,
>>> Euclid's algorithm just works.
>>> [...]
>>> If it were more work to support non-integer inputs, I'd say that it's
>>> not worth the effort, but since it's actually less work to just allow
>>> it, then why not?
>>
>> Okay, I allow that now, but I've still left it for lcm. I can't find
>> anything anywhere that defines lcm for floating point (I do find it for
>> fractions) and the result of abs(a*b)/gcd(a,b) certainly doesn't match
>> "lowest" in the examples I tried.
>>
> Here's another article on the subject:
> https://www.math-only-math.com/hcf-and-lcm-of-decimals.html

Yeah, my eyes weren't aligning the decimal points properly.

Attached version frees up lcm to work on non-integrals.  Thanks for your
input!

--

Vik Fearing

Attachment Content-Type Size
gcd.0007.patch text/x-patch 23.4 KB

In response to

Responses

Browse pgsql-hackers by date

  From Date Subject
Next Message Tomas Vondra 2020-01-04 22:00:54 Re: [HACKERS] Re: [COMMITTERS] pgsql: Remove pgbench "progress" test pending solution of its timing is (fwd)
Previous Message Fabien COELHO 2020-01-04 21:21:15 Re: Greatest Common Divisor