Algorithm for IRI-to-URI/URI-to-IRI conversion

Are there any open source algorithms for converting an IRI to an URI and an开发者_开发百科 URI to an IRI?

A C# implementation is preferable, but not necessary.

.NET 2.0 SP1 and later has built in support for IRI: http://msdn.microsoft.com/en-us/library/bb968786.aspx