Proof Of Concept PatchUtility to be use in MFC/C++ Program

I am in need for a Library Toolkit to create Patch files for the different file deliveries i have to my clients.? This program can be in a dll or lib and should be one time payment for its usage.? Basically I need some very simple api to compare two files and create a delta file which represent the difference between the two files.? I don't need a comparing directories just a file to file level is all i need.? If you know of any utilities/packages that can be used that would be great.? I do need to distribute this lib or dll with my program and it needs to run at client machines.? I am sure this type of libraries/programs exist out there; just needs a simple executable and source code to demonstrate this can be done... ## Deliverables I am not looking for somebody to write the patch utility ; if u can show me an patch utility out there that is royalty free that is fine and that i can use on multiple client machines to create these deltas and make the job of receiving my information easier/faster .