Serialization of floating point values to XML: Remove superfluous handling of special values

[mtx500]

Proposed changes

In OPC UA the serialization of floating point values to XML just follows the XML Schema specification (see https://www.w3.org/TR/xmlschema-2/#float). It is sufficient to use the correct .NET XML classes (XmlReader, XmlWriter, XmlConvert). There is no need to treat the special values Infinity, negative Infinity and Not-a-number in special way.

XmlWriter uses XmlConvert internally (see https://referencesource.microsoft.com/#System.Xml/System/Xml/Core/XmlWriter.cs and https://github.com/dotnet/runtime/blob/main/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriter.cs), and XmlConvert (see https://referencesource.microsoft.com/#System.Xml/System/Xml/XmlConvert.cs and https://github.com/dotnet/runtime/blob/main/src/libraries/System.Private.Xml/src/System/Xml/XmlConvert.cs) first takes care of "INF" and "-INF" and then uses the Single / Double routines with the appropriate flags and culture set so that "NaN" is also taken care of.

BTW, the removed code parts were inconsistent:

• not all routines contained the special treatment of the special values
• Double values were set with the special Single constants

Types of changes

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• [ ] Bugfix (non-breaking change which fixes an issue)
• [ ] Enhancement (non-breaking change which adds functionality)
• [ ] Test enhancement (non-breaking change to increase test coverage)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected, requires version increase of Nuget packages)
• [ ] Documentation Update (if none of the other choices apply)
• [x] Optimization (no functional change)

Checklist

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• [x] I have read the CONTRIBUTING doc.
• [x] I have signed the CLA.
• [x] I ran tests locally with my changes, all passed.
• [ ] I fixed all failing tests in the CI pipelines.
• [ ] I fixed all introduced issues with CodeQL and LGTM.
• [ ] I have added tests that prove my fix is effective or that my feature works and increased code coverage.
• [ ] I have added necessary documentation (if appropriate).
• [ ] Any dependent changes have been merged and published in downstream modules.

Further comments

[romanett]

Thanks for the additions. Can you add some simple Unit Tests proving the edge cases are handled correctly on all platforms / build targets?

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 54.62%. Comparing base (414a0d5) to head (8dcbbde).

Files	Patch %	Lines
Stack/Opc.Ua.Core/Types/Encoders/XmlDecoder.cs	66.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2588 +/- ## ======================================= Coverage 54.62% 54.62% ======================================= Files 342 342 Lines 65082 65056 -26 Branches 13350 13335 -15 ======================================= - Hits 35548 35539 -9 + Misses 25663 25649 -14 + Partials 3871 3868 -3 ```

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[mtx500]

I will create unit testing. As I am doing this the first time, it takes a little bit ...

[mtx500]

Should be finished and OK now. The still failing tests seem to me not being effected by my changes.

[mregen]

@opcfoundation-org as this change may affect nodeset generation please code review this change to Xml encoder and decoder.