[Oledb-dev] [HACKERS] Re: double precision error with pg linux server, but not with windows pg server

[Tom Lane]

Shachar Shemesh <shachar at shemesh.biz> writes:
> Tom Lane wrote:
>> Binary format has other goals that are not always compatible with 100%
>> platform independence --- that's unfortunate, sure, but it's reality.
>> 
> Maybe the misunderstanding is mine. What are the goals for the binary
> format?

Well, the one that I'm concerned about at the moment is that dump/reload
using COPY BINARY ought to be 100% guaranteed to reproduce the original
datum.

Obviously, if you are transporting the dump across platforms then that
may be an impossibility.  In that case you use a text dump and accept
that you get an approximation.  But there should be a way to ensure that
you can have a lossless dump of whatever strange FP format your server
may use, as long as you are restoring onto a similar machine.

If there is a guaranteed-reversible transform between the ARM FP format
and IEEE format, then I'd be interested in hacking things the way you
suggest --- but what I suspect is that such a conversion must lose
either range or precision.  There are only so many bits in a double.

			regards, tom lane