Subject: Re: Greatest Common Divisor
To: Fabien COELHO <coelho@cri.ensmp.fr>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Stephen Frost <sfrost@snowman.net>,
 Dean Rasheed <dean.a.rasheed@gmail.com>,
 Chapman Flack <chap@anastigmatix.net>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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From: Vik Fearing <vik.fearing@2ndquadrant.com>
Message-ID: <5bf72c6b-1290-2ba0-770b-8a13e899fd98@2ndquadrant.com>
Date: Fri, 3 Jan 2020 23:57:54 +0100
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On 03/01/2020 20:14, Fabien COELHO wrote:
>
> Bonsoir Vik,
>
>  +int4gcd_internal(int32 arg1, int32 arg2)
>  +{
>  +       int32   swap;
>  +
>  +       /*
>  +        * Put the greater value in arg1.
>  +        * This would happen automatically in the loop below, but
> avoids  an
>  +        * expensive modulo simulation on some architectures.
>  +        */
>  +       if (arg1 < arg2)
>  +       {
>  +               swap = arg1;
>  +               arg1 = arg2;
>  +               arg2 = swap;
>  +       }
>
>
> The point of swapping is to a void possibly expensive modulo, but this
> should be done on absolute values, otherwise it may not achieve its
> purpose as stated by the comment?


Ah, true.  How widespread are these architectures that need this special
treatment?  Is it really worth handling?


> I'm unsure about gcd(INT_MIN, 0) should error. Possibly 0 would be nicer?


What justification for that do you have?

-- 

Vik Fearing