Re: add modulo (%) operator to pgbench - Mailing list pgsql-hackers

From Fabien COELHO
Subject Re: add modulo (%) operator to pgbench
Date
Msg-id alpine.DEB.2.10.1408060814010.24380@sto
Whole thread Raw
In response to Re: add modulo (%) operator to pgbench  (Robert Haas <robertmhaas@gmail.com>)
List pgsql-hackers
Hello Robert,

>> The issue is that there are 3 definitions of modulo, two of which are fine
>> (Knuth floored division and Euclidian), and the last one much less useful.
>> Alas, C (%) & SQL (MOD) choose the bad definition:-( I really need any of
>> the other two. The attached patch adds all versions, with "%" and "mod"
>> consistent with their C and SQL unfortunate counterparts, and "fmod" and
>> "emod" the sane ones.
>
> Three different modulo operators seems like a lot for a language that
> doesn't even have a real expression syntax, but I'll yield to whatever
> the consensus is on this one.

I agree that it is overkill.

In fact there is a link: if there was a real expression syntax, the 
remainder sign could be fixed afterwards, so the standard C/SQL version 
would do. If it is not available, the modulo operator must be right.

If there is only one modulo added, I would rather have the Knuth version. 
However I was afraid that someone would object if "%" does not return the 
same result than the C/PostgreSQL versions (even if I think that nearly 
nobody has a clue about what % returns when arguments are negative), hence 
the 3 modulo version to counter this potential critic.

But I would prefer just one version with the Knuth (or Euclidian)
definitions.

-- 
Fabien.



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