The file format is documented in smx-headers.h, smx-v1-opcodes.h, and smx-v1.h here:
https://github.com/alliedmodders/sou...er/include/smx
There's a reference implementation of the VM in interpreter.cpp.
We have another repo, "smxtools" (should probably be merged into the SP repo):
https://github.com/alliedmodders/smxtools
It's basically a C# implementation of everything but the VM, and it's a bit easier to read than the C++ code.