Re: Greatest Common Divisor

From: Vik Fearing <vik(dot)fearing(at)2ndquadrant(dot)com>
To: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, 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 02:32:34
Message-ID: 32b8af34-8f87-c30f-5555-2325bd140a59@2ndquadrant.com
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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?

Here is an updated patch fixing that.

--

Vik Fearing

Attachment Content-Type Size
gcd.0005.patch text/x-patch 23.6 KB

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