Re: ERROR: value out of range: underflow in numeric log calculation

Gallacher Neil <Neil(dot)Gallacher(at)gstt(dot)nhs(dot)uk> writes:
> When executing log calculations (example below):
> SELECT 1.0 * exp(-1.0 *(ln(2) * (1695993520/86400.0)) / 0.04) AS result_test;
> The following error occurs.
> ERROR: value out of range: underflow

Yup.

> I can however understand that an individual might wish to know that the result of a calculation cannot be represented by the system due to its small value however I don't believe it should be the default behaviour.

You'd be in a minority on that opinion. In this case you could work
around it by asking for the calculation to be done in numeric rather
than float8:

regression=# SELECT 1.0 * exp(-1.0 *(ln(2::numeric) * (1695993520/86400.0)) / 0.04) AS result_test;
result_test
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
(1 row)

but I'm not sure how far that covers your real use-case.

regards, tom lane