Re: pow support for pgbench

From: Raúl Marín Rodríguez <rmrodriguez(at)carto(dot)com>
To: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
Cc: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pow support for pgbench
Date: 2017-11-06 11:41:06
Message-ID: CAM6_UM45MSRq_2MDfCOEFwjA0-NYzJLe11-sKgF7ZfncErTPgw@mail.gmail.com
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Hi Fabien,

Thanks for the review.
I've fixed the documentation and added an ipow function that handles both
positive and negative ints, having 0^0 == 1 and 0^(negative) == PG_INT64_MAX
since that's what my glibc math.h pow() is returning.

On Sat, Nov 4, 2017 at 12:34 PM, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> wrote:

>
> Hello Raúl,
>
> Sorry about the patch. Attaching it now so it can be considered as
>> submitted.
>>
>
> There is a typo in the XML doc:
>
> <literal>1024.0/<literal>
>
> Please check that the documentation compiles.
>
> I'm at odds with having the integer version rely on a double pow(), even
> if it works. I think that there should be a specific integer version which
> does use integer operations. From stack overflow, the following is
> suggested:
>
> int ipow(int base, int exp)
> {
> int result = 1;
> while (exp)
> {
> if (exp & 1)
> result *= base;
> exp >>= 1;
> base *= base;
> }
>
> return result;
> }
>
> The integer version should be when x & y are integers *AND* y >= 0.
>
> if y is a negative integer, the double version should be used.
>
> --
> Fabien.

--

*Raúl Marín Rodríguez*carto.com

Attachment Content-Type Size
pgbench_pow_v3_pgbench-more-ops-funcs-14.patch text/x-patch 4.6 KB

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