As others already said, XS is compiled C code.

There are a few options, depending on what exactly you mean by "checking the code" (I'm assuming Linux here, although most/all of this should also work on Windows with the correct tools installed):

• strings shows you all the assumed plain text in the file.
• objdump let's you dump all kind of stuff from a binary or library.
• You might need a decompiler, for example Boomerang.
• If you got the money, go for Hex-Rays.