When writing the Microtan 65 emulator, which subsequently expanded to be a CHIP-8 and Space Invaders emulator too, I wanted to be able to check resource files when loaded to ensure they were uncorrupted. The easiest way to do this was to determine their checksum when ok, and then check this was unchanged every time they were loaded. To do this I wrote a simple little program that allowed you to drop a file on its window, and it would calculate the CRC32 checksum which could then be used in the program.