License question: what constitutes a "redistribution of source code"?

Hello,

I am one of the developers of the Open Toolkit (http://www.opentk.com),
a game development library available under the MIT/X11 license.

As part of our math toolkit, we would like to support half-precision
numbers. Our Half type contains two methods, ToSingle and FromSingle,
which were derived from the OpenEXR implementation, after omitting the
lookup tables and rewriting them in C#.

Does this constitute a "redistribution of source code", as per the first
term of the OpenEXR license?