Good evening,

While experimenting with assembler, I ran into a problem of comparing two files of equal size. The "original" and "patched" version.

I wrote two simple programmes in order to do that:
1. fcompare - compares 2 files and writes the result to the *.fcp file.
2. fcp - opens the *.fcp file, searches for original programme with human help, and then turns it magically into fixed version.

I reused the error reporting technique that Tomasz used in FA.asm and some code regarding file operations from fasm\TOOLS\WIN32\SYSTEM.INC.

Structure of *.fcp file:

Size of Entry - 6 bytes
Maximum number of entries in *.fcp file is 65536.

Hence, maximum *.fcp file size is 14 + (1..260) + 65536*6 = 393230..393489 bytes.

The limit for size of patched file to compare is 100 Mb. Programme reads the whole two files into memory, that might be bad practice, I did consider using 64k blocks for compare procedure, but I was lazy to implement it.

I tested it on number of files, but I might have missed some bugs, so it would be wonderful if you could report bugs in this thread. Or you can fix them yourself. I'm attaching full sources.

I know I'm not the first to write such thing, but I want to hope that it will be useful for the ASM society.

Thanks for your attention.

One way also is to use the hashing technique.

I would sell this program to Microsoft. For the next patch day.

This is the standalone patch generator. You compile it specifying a file include directive @ patch_data label (see source). After that patch file is included in exe. You can distribute it afterwards, for example.

At first I tried to combine them with copy /b, but when programme starts, windows loads just what is specified in the header of EXE file. I was lazy to dig the PE specification.