How to convert from base-256 to base-N, where N is higher than 16?

I need to convert an array of bytes to another base, namely 85. In math terms the question is how to convert from开发者_如何学C base-256 to base-85 in the most efficient way?

This question is inspired by my previous question - What is the most efficient way to encode an arbitrary GUID into readable ASCII (33-127)?

Thanks.

You mean like this? http://www.codinghorror.com/blog/2005/10/c-implementation-of-ascii85.html