Horton

Re: factorial of negative numbers

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2020-06-15T13:59:21Z
Lists: pgsql-hackers 
Peter Eisentraut <peter.eisentraut@2ndquadrant.com> writes:
> Adjacent to the discussion in [0] I wanted to document the factorial() 
> function and expand the tests for that slightly with some edge cases.
> ...
> I propose to change this to error out for negative numbers.

+1 for all of this, with a couple trivial nitpicks about the error
changes:

* I'd have written the error as "factorial of a negative number is
undefined" ... not sure what a grammar stickler would say about it,
but that seems more natural to me.

* I'd leave the "if (num <= 1)" test after the error check as-is;
it's probably a shade cheaper than "if (num == 0 || num == 1)".

			regards, tom lane

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