Compare the file file1 with the file file2. If they differ in size, print the sizes like this:
Differ in size: 0x1234 [foo], 0x4321 [bar]
If the sizes are equal but the bytes at an offset differ, then print the bytes like this:
Differ at the offset 777: 0xbe [foo], 0xef [bar]
If they are completely identical, nothing will be printed.