Add Callback parameter to C function

Hello Coders, I have a library which process input data (giving a pointer to data and data size). I just call a function in the library to process all input data. I would like to extend that function in the library to accept a Callback, so my Callback is called periodically (let's say each 128+ bytes processed) to know the amount of current data processed. The library is coded in C/C++ and I have already a working DLL (with source code also) which uses that library. If you have interested in this project, let me know. Thanks!