Re: gamma() and lgamma() functions

On Thu, 14 Nov 2024 at 22:35, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> wrote:
>
> On Thu, 14 Nov 2024 at 16:28, Dmitry Koval <d(dot)koval(at)postgrespro(dot)ru> wrote:
> >
> > >SELECT gamma(float8 '1e-320');
> > ERROR: value out of range: overflow
> >
> > >SELECT gamma(float8 '0');
> > gamma
> > ----------
> > Infinity
> > (1 row)
> >
> > Perhaps it would be logical if the behavior in these cases was the same
> > (either ERROR or 'Infinity')?
>
> In general, I think that having gamma() throw overflow errors is
> useful for spotting real problems in user code.
>

Thinking about this afresh, I remain of the opinion that having the
gamma function throw overflow errors is useful for inputs that are too
large, like gamma(200). But then, if we're going to do that, maybe we
should just do the same for other invalid inputs (zero, negative
integers, and -Inf). That resolves the consistency issue with inputs
very close to zero, and seems like a practical solution.

Attached is an update doing that.

Regards,
Dean