Re: pow support for pgbench

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: Raúl Marín Rodríguez <rmrodriguez(at)carto(dot)com>
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: 2017-11-04 11:34:52
Message-ID: alpine.DEB.2.20.1711041223391.14090@lancre
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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.

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