the best thing about ghidra is that no matter which version you're using, setting equates sometimes just doesn't work, but if you google it, you only find several bug reports which basically say "equates don't work" and then it's "closed, fixed in X.Y.Z" and that's a version you're upgraded way past

port_out(0x3c4,0xf02);

I SO WANT TO EQUATE 0x3C4 TO THE VGA SEQUENCER INDEX REGISTER BUT I CAN'T

the weird thing is the equates table says it's been set, says there's a reference to it at that address, but if I go to that address, there's nothing. just 0x3c4
OH GOODY I found a mistake in OSDEV
their docs on the PC gameport are incorrect
and I can't rename some local variables either!?
what the fuck, ghidra?

okay I've fixed OSDEV:
https://wiki.osdev.org/Game_port

They had the introduction of the gameport listed as "the PCjr" (it's from 1981, the PCjr came out in 1984... and didn't even have this gameport connector!) but more importantly, they had the order of the joystick axises wrong.

Game port - OSDev Wiki

and the IBM Game Control Adapter is mentioned in the August 1981 IBM PC Technical Reference, so IBM clearly had the gameport ready at day one of the IBM PC, even if it was an optional add-in.
mind you, on the IBM PC, just about everything is an optional add-in. You get a keyboard and a cassette port for free: you want graphics/text, floppies, hard drives, serial/parallel ports? that's extra.

god. Duke Nukem 1 has so much copy-pasted code.
Like, there's a ton of hint dialog boxes like "You need the key to open this door!" or "you get more points if you catch the balloon"

you'd think they'd just have ShowMessage() and pass it a different string, but nope. it's a different function.

LEARN TO WRITE REUSABLE FUNCTIONS

interesting. there's 12 hint-variables which are used to make sure you don't get hinted for something you've used before.

One of them is still maintained, but not used. So there must have been another hintable thing that got dropped

although I'm looking at DN1, episode 1. Maybe it does do something in DN1E2 or DN1E3?
because yeah this was also the era where you'd have 3 separate executables for 3 separate episodes of the same game

like, it has a function that loops through all 16 color indices and sets them to black. it takes one parameters, which tells it how long to wait between each color is set, so it'll fade slowly to black, instead of being instant.

there's also an identical function that does the same, but sets it to white, instead.

so instead of fade_screen(COLOR_BLACK) and fade_screen(COLOR_WHITE), it's two separate functions!
naturally instead of a function like "adjust_duke_health(n)" there's a "give_duke_one_health_point" function
todd replogle: look, I know programmers who use function parameters and data-driven design, and they're all cowards
The game starts with these two screens.
There's a function to draw Dr Proton, a different function to draw Duke Nukem, a function to draw Proton's text, and another function to draw Duke's

the only difference between the "draw proton"/"draw duke" functions is what base address they draw from.

YOU CAN PASS ADDRESSES TO FUNCTIONS, TODD

@foone There are languages/formalisms where you can only pass one parameter to a function.

Maybe they were working in a language where you can't pass *any* parameters to a function?

I'm sure there's some mathematician that's managed it. Somewhere.

@darkling you'd think, but nope! this was compiled with Borland Turbo C.
@foone ... I've got nothing. 
@foone @darkling
Is it possible this is some segmented memory/near/far pointer thing?
Maybe not even the coder did this, but Borland decided to duplicate the function for some reason.

@poeschel @foone At this point, I'm talking out of my arse (I'm not really an x86 person), but it's duplicating a significant amount of code to avoid passing a single (possibly-)far pointer where it could avoid the duplication at the cost of passing one far pointer? Seems like a significant mis-optimisation on the part of the compiler.

Maybe a segment change is massively more expensive than I think it is, but I hope it isn't that bad.

@darkling @poeschel yeah, I don't think that's the case. all 5 are in the same code segment, addressing the same data segment.