Re: Significant Digits in Floating Point Datatype

On 11/20/2011 02:06 PM, Tom Lane wrote:
> Lee Hachadoorian<lee.hachadoorian@gmail.com>  writes:
>> And can I reliably retrieve the original integer by
>> casting to int (or bigint) if the number of digits in the original
>> integer is less than 15?
> On IEEE-floating-point machines, I'd expect float8 to store integers
> up to 2^52 (or maybe it's 2^53) exactly.  With other floating-point
> formats the limit might be different, but it should still be exact for
> reasonable-size integers.  This has nothing whatever to do with whether
> decimal fractions are reproduced exactly (in general, they aren't, no
> matter how many or few digits are involved).  So integers are fine,
> bigints not so much.
>
>             regards, tom lane

Thank you, that clarification is extremely useful.  --Lee

--
Lee Hachadoorian
PhD, Earth&  Environmental Sciences (Geography)
Research Associate, CUNY Center for Urban Research
http://freecity.commons.gc.cuny.edu