Ahh - what I was missing was the actual requirements! 🙂

This may get you part-way there: http://pratchev.blogspot.com/2008/04/convert-hex-string-to-binary-string.html. You will need to efficiently deal with leading zeros though before doing the reverse/replace thing. The key is to do this as a set-based operation and not the iterative way you have now. I am confident there is a solution, but it goes beyond what I am willing to invest for free to get you there. 😎