Re: float output precision questions

Stephan Szabo wrote:
> On Tue, 29 Oct 2002, Peter Eisentraut wrote:
>
>
>>Pedro Miguel Frazao Fernandes Ferreira writes:
>>
>>
>>>Is there a way to set query output precision to maximum precision ?
>>>For the type of application I mentioned this is crucial. People want to
>>>get the 'same' numbers, from querys or dumps, as they inserted them.
>>
>
> How do you define maximum precision and "same"? With simple test programs
> in C, using two digits more than DBL_DIG for printf specifier, it's easy
> for me to find numbers that "change" decimal string representation in the
> decimal representation -> double -> decimal representation conversion(*).
> The final double you get from the second conversion should be the same as
> the first, but is that what you need or do you need a stronger guarantee
> than that?

When I say "same" I am talking about having a number 'stored' in double
format in some client, inserting it in PostgreSQL float8 field and get
it to the client as it was before:

[Some client] (insert) [PostgreSQL] (query) [Some client]
(double number a)-------->(float8 number)------->(double number b)

"same" is so that a==b is true.
With current float8 output this is not allways true.

I believe this should allways be true for numbers which are originally
stored in double format.

Thanks,
Pedro M. Ferreira

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--
----------------------------------------------------------------------
Pedro Miguel Frazao Fernandes Ferreira
Universidade do Algarve
Faculdade de Ciencias e Tecnologia
Campus de Gambelas
8000-117 Faro
Portugal
Tel./Fax: (+351) 289 800950 / 289 819403
http://w3.ualg.pt/~pfrazao