Re: round(x) function

On 3/26/2010 12:12 PM, Tom Lane wrote:
> "Gaietti, Mauro \(SELEX GALILEO Guest, Italy\)"<mauro(dot)gaietti(at)guests(dot)selexgalileo(dot)com> writes:
>
>> This query:
>> select round(0.5), round(0.5::integer), round(0.5::bigint), round(
>> 0.5::float ), round( 0.5::double precision ),round(cast(0.5 as double
>> precision )),round(cast(0.5::double precision as numeric )); has strange
>> result:
>> 1 1 1 0 0 0 1
>>
>> Is this correct?
>>
> On most machines the float4/float8 operations follow the IEEE-754 spec's
> "round to nearest even" rule for such cases. I think all the other ones
> are "add 0.5 and truncate" implementations. It's unlikely we'll mess
> with either; and *highly* unlikely that we would change the float
> behavior since that's not even under our direct control (the hardware or
> libm is what's doing that). There's some case to be made for making
> numeric and integer math do it the IEEE way, but I think that would
> displease at least as many people as it pleased ...
>
> regards, tom lane
>
>
This topic keeps coming up every few months about rounding which way is
correct. I would be in favor of adding a option to round() function to
specify method.

Leave the defaults as they are for backwards capability, meaning if no
option is passed to Round() it follows current methods. I agree
changing how it works now would annoy many.

The option would be very simple something like this
Round( 0.5, RoundToEven) = 0
Round( -0.5, RoundToEven) = 0
Round(0.5, RoundUp) = 1
Round(-0.5, RoundUp) = 0
Round(0.5, RoundDown) = 0
Round(-0.5, RoundDown) = -1
Round(0.5, RoundToZero) = 0
Round(-0.5, RoundToZero) = 0

There are so many methods of rounding to choose from
http://en.wikipedia.org/wiki/Rounding

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