⮜ Blog

📝 Posted:
🚚 Summary of:
P0066
⌨ Commits:
042b780...e55a48b
💰 Funded by:
Yanga, Splashman

So, the thing that made me so excited about TH01 were all those bulky C reimplementations of master.lib functions. Identical copies in all three executables, trivial to figure out and decompile, removing tons of instructions, and providing a foundation for large parts of the game later. The first set of functions near the end of that shared code segment deals with color palette handling, and master.lib's resident palette structure in particular. (No relation to the game's resident structure.) Which directly starts us out with pretty much all the decompilation difficulties imaginable:

  • iteration over internal DOS structures via segment pointers – Turbo C++ doesn't support a lot of arithmetic on those, requiring tons of casts to make it work
  • calls to a far function near the beginning of a segment from a function near the end of a segment – these are undecompilable until we've decompiled both functions (and thus, the majority of the segment), and need to be spelled out in ASM for the time being. And if the caller then stores some of the involved variables in registers, there's no way around the ugliest of workarounds, spelling out opcode bytes…
  • surprising color format inconsistencies – apparently, GRB (rather than RGB) is some sort of wider standard in PC-98 inter-process communication, because it matches the order of the hardware's palette register ports? (0AAh = green, 0ACh = red, 0AEh = blue)? Yet the game's actual palette still uses RGB…

And as it turns out, the game doesn't even use the resident palette feature. Which adds yet another set of functions to the, uh, learning experience that ZUN must have chosen this game to be. I wouldn't be surprised if we manage to uncover actual scrapped beta game content later on, among all the unused code that's bound to still be in there.

At least decompilation should get easier for the next few TH01 pushes now… right?