Re: pgsql: Add support for hyperbolic functions, as well as log10().

On Wed, 13 Mar 2019, 21:56 Tom Lane, <tgl@sss.pgh.pa.us> wrote:

>
> Of these, probably the least bad is #3, even though it might require
> a few rounds of experimentation to find the best extra_float_digits
> setting to use.  I'll go try it without any roundoff, just to see
> what the raw results look like ...
>


Yeah, that seems like a reasonable thing to try.

I'm amazed that jacana's asinh() returned -0 for an input of +0. I'm not
aware of any implementation that does that. I'd be quite interested to know
what it returned for an input like 1e-20. If that returned any variety of
zero, I'd say that it's worse than useless. Another interesting test case
would be whether or not it satisfies asinh(-x) = -asinh(x) for a variety of
different values of x, because that's something that commonly breaks down
badly with naive implementations.

It's not unreasonable to expect these functions to be accurate to within
the last 1 or 2 digits, so testing with extra_float_digits or whatever
seems reasonable, but I think a wider variety of test inputs is required.

I also wonder if we should be doing what we do for the regular trig
functions and explicitly handle special cases like Inf and NaN to ensure
POSIX compatibility on all platforms.

Regards,
Dean


>