Re: [COMMITTERS] pgsql: Add trigonometric functions that work in degrees.

Noah Misch <noah(at)leadboat(dot)com> writes:
> On Mon, Apr 18, 2016 at 09:17:46AM -0400, Tom Lane wrote:
>> Given that it's apparently showing the results of asind as NULL ...

> I doubt asind is returning NULL. Here's the query, which uses a CASE to
> report NULL if asind returns any value not on a whitelist:

> SELECT x,
> CASE WHEN asind(x) IN (-90,-30,0,30,90) THEN asind(x) END AS asind,
> CASE WHEN acosd(x) IN (0,60,90,120,180) THEN acosd(x) END AS acosd,
> CASE WHEN atand(x) IN (-45,0,45) THEN atand(x) END AS atand
> FROM (VALUES (-1), (-0.5), (0), (0.5), (1)) AS t(x);

Oh, duh --- should have checked the query. Yes, the most probable theory
must be that it's returning something that's slightly off from the exact
value.

> I can see the benefit for atand(-0.5) and for atand(0.5), since those are
> inexact. Does the CASE gain us anything for asind or acosd?

None of these are expected to be inexact. The point of the CASE is to
make it obvious if what's returned isn't *exactly* what we expect.

We could alternatively set extra_float_digits to its max value and hope
that off-by-one-in-the-last-place values would get printed as something
visibly different from the exact result. I'm not sure I want to trust
that that works reliably; but maybe it would be worth printing the
result both ways, just to provide additional info when there's a failure.

regards, tom lane