Horton

Re: factorial of negative numbers

Dean Rasheed <dean.a.rasheed@gmail.com>

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From: Dean Rasheed <dean.a.rasheed@gmail.com>
To: Juan José Santamaría Flecha <juanjo.santamaria@gmail.com>
Cc: Bruce Momjian <bruce@momjian.us>, Ashutosh Bapat <ashutosh.bapat@2ndquadrant.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2020-06-16T09:49:59Z
Lists: pgsql-hackers 
On Tue, 16 Jun 2020 at 10:09, Juan José Santamaría Flecha
<juanjo.santamaria@gmail.com> wrote:
>
> It is defined as NaN (or undefined), which is not in the realm of integer numbers. You might get a clear idea of the logic from [1], where they also make a case for the error being ERRCODE_DIVISION_BY_ZERO.
>
> [1] http://mathforum.org/library/drmath/view/60851.html
>

Hmm, I think ERRCODE_DIVISION_BY_ZERO should probably be reserved for
actual division functions.

With [1], we could return 'Infinity', which would be more correct from
a mathematical point of view, and might be preferable to erroring-out
in some contexts.

[1] https://www.postgresql.org/message-id/606717.1591924582%40sss.pgh.pa.us

Regards,
Dean

Commits

  1. Disallow factorial of negative numbers

  2. Expand tests for factorial

  3. doc: Document factorial function

  4. Attached is a patch implementing factorial(), returning numeric. Points