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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-- 
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Pedro Miguel Frazao Fernandes Ferreira
Universidade do Algarve
Faculdade de Ciencias e Tecnologia
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