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From Caroline Maynard <...@php.net>
Subject [SDO][C++] Float / double loss of precision
Date Thu, 19 Jun 2008 23:32:07 GMT
A PHP SCA/SDO user has observed a problem when working with a schema 
that uses floating point types.

Everything is fine when we read the data from Tuscany as a floating 
point type. But when Tuscany converts the data to a string, then it 
loses precision, and in particular this happens when the data is written 
to an XML document.

When Tuscany does this conversion, it uses a format string of "%.3Le" 
for a double, or "%.3e" for a float. This means that it will always use 
scientific notation, with only 3 decimal places, resulting in 
significant loss of precision.

I did check this against the SDO 2.1 spec, and that expects doubles and 
floats to be printed as [0-9]*('.'[0-9])?('E'|'e'). So I don't know why 
Tuscany chose its format. Certainly not from the XML schema spec: 
http://www.w3.org/TR/xmlschema-2/#float.

Is there anyone still around who can shed any light on why Tuscany does 
this? Do you agree it's a problem? I'm guessing that that raising a JIRA 
isn't going to get me a fix, but if I develop a patch myself, would 
someone volunteer to apply it?

(You'll recall that in PHP we are using the sdo-cpp-pre2.1 branch, but 
the same format string is used in trunk, so the problem applies there too.)



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