I wrote a wrapper around Lucene.Net to provide simple API access to some very basic operations (index, search, delete) that will be used by a Delphi Win32 application. Everything was working fine, but deep in the bowels of the Lucene code, in one code path, I encountered a line like this:

      return (float) (System.Math.Log(numDocs / (double) (docFreq + 1)) + 1.0);

When there are no documents in the index, this essentially evaluates to a call to System.Math.Log(0.0), which according to the MSDN documentation, should return NegativeInfinity. In fact, when this library is called from a .NET client, it does just that. However, when called via COM interop, this results in an exception, "Attempted to divide by zero". I started to modify the Lucene source to do a check for this condition and just manually return NegativeInfinity, and that did get me past that point, but then later on in the Lucene code, I end up getting an "Arithmetic overflow/underflow" error when Lucene tries to do some math on the returned value. So rather than continue to band-aid this problem, I thought I'd try to dig to the root of the problem to see why this is happening.

You can find an extremely simple test case with a .NET Class Library, .NET test client, and Delphi test client here. Just build the .NET solution, and then you can run the createtlb.bat file in the LogClient directory to get the Delphi project ready.