jonesforth VS DOOM

Cool. Here are some other resources that I've encountered along the way of learning Forth:

- JonesForth: https://github.com/nornagon/jonesforth/blob/master/jonesfort...

This is legit a text that goes the an x86 Forth implementation. Actually, it's just an implementation with really extensive comments. That said, including whitespace and comments, it's just 2000 lines and the pedagogy is excellent. Highly recommended for anyone who would rather see behind the curtain before picking up a larger text.

- SmithForth: https://dacvs.neocities.org/SF/

So, Smith decided to hand-write a Forth directly in x86-64 opcodes (well, the corresponding ascii hex bytes). It's incredibly slim and enlightening how you can bootstrap a language in just a couple hundred bytes or so.

This project actually inspired me to really learn the x86-64 architecture, so I ended up hand-decompiling the SmithForth binary instead of going through his commented implementation. Hand-decompilation is an absolutely fascinating exercise. You learn all about ELF structure, opcode encodings, and actually start to see the gaps where microarchitectural details shine through. Highly recommended for any hacker that really wants to grok low level details.

- Mecrisp: https://mecrisp.sourceforge.net/

An amazingly fast Forth implementation for MSP430, ARM, RISC-V, MIPS, and some FPGAs. This gave me one really nice understanding of Forth as

    A REPL into your hardware!

I've git-cloned JonesFORTH (https://github.com/nornagon/jonesforth/blob/master/jonesforth.S) and achieved to compile it (i.e. run make w/o an error. When I start the executable, it presents me with an empty line, and when I say BYE, it says PARSE ERROR: bye.

Is there any particular language you're looking for? I've found some languages hideous until I understood them and could appreciate their respective graces. Off the top of my head the I can think of a couple.

The first is Jones Forth (https://github.com/nornagon/jonesforth), start with jonesforth.S and move into jonesforth.f. I really enjoyed following along with it and trying my hand at making my own stack based language.

The other is Xv6, a teaching operating system from MIT (https://pdos.csail.mit.edu/6.828/2021/xv6.html), not all the code or implementations are top notch but it shows you non-optimized versions (just because they're simple and more readable) of different concepts used in OS design.

If you're interested in the embedded world, there is a really neat project I've been following that feels a more structured and safe (as in fault-tolerant) while still staying pretty simple (both conceptually and in the code itself): Hubris and Humility (https://hubris.oxide.computer/).

Very low hardware requirements, so basic industrial control at the level where you'd otherwise use an Arduino or so but on scavenged hardware. Forth is ridiculously simple to get an implementation running.

https://github.com/nornagon/jonesforth/blob/master/jonesfort...

Is a nice starting point. It's obviously not as compact as say 'Brainfuck' but it is far more versatile.

OP mentioned jonesforth, but linked to a nasm port of it. Which is probably good it’s just that the documentation in the comments with ascii art doesn’t look right on my screen. So here’s a more common repo: https://github.com/nornagon/jonesforth

Rip the asm macros for the basic FORTH words out of this and then embed them in a C binary, statically linked with your favourite libs for whatever task. Although I haven't tried this yet, I'm planning on doing it with ncurses for my own Roguelike. From there, if you can convert the function calls and your parameters down to raw numbers, you can send instructions to ncurses or whatever other API you like, directly from a FORTH stack.

or the mirror of this site in github: https://github.com/nornagon/jonesforth

commercially exploit or use for any commercial purpose."

[1] https://github.com/id-Software/DOOM/commit/4eb368a960647c8cc...

The original Doom had third-party audio playback routines, so the source came with a rewritten sound server: https://github.com/id-Software/DOOM/tree/master/sndserv

    The bad news:  this code only compiles and runs on linux.  We couldn't

Here's a repo for you with no test coverage and no auto-generated DI. They using unsafe pointers all over the place, too!

https://github.com/id-Software/DOOM

Shall I prepare the postage for the letter in which you'll call John Carmack an MBA? Should we send another to Chris Sawyer? I heard he didn't even write a formal design doc for Roller Coaster Tycoon!

cURL is one of the most used C libs and is an example of good quality C code. If you follow the style used there, see e.g. https://github.com/curl/curl/blob/master/lib/dynhds.h (and associated dynhds.c) you will be good.

Looking at the source of some of the old game-engines from the era that have since been released as open-source can also be helpful, like https://github.com/id-Software/DOOM.

In both cases notice how simple and elegant a lot of the code is. There is already enough complexity inherent in the problem they are solving, and that is where the focus should be.

Any IDE with a working language server to make it easy to jump around and refactor should work fine. Limitations might be due to the C language itself?

Error handling on such a fixed platform does not need to be super-advanced. You should always be within the confines of the system so there shouldn't be much that can go wrong. If stuff goes wrong anyway just being able call a function Fatal("FooBar failed with code 34") when unexpected stuff happens and have it log somewhere to be able to dig around should be enough. You never need to be able to recover and retry.

Make sure to use https://clang.llvm.org/docs/AddressSanitizer.html or a similar tool when developing outside of the PSOne.

That said, consider statically allocating global buffers for most stuff and avoid using the heap for most stuff.

Good luck working within the confines of the PSOne! Many hackers have pulled the hair from their head on that platform ;)

Probably more easily than you'd think. DOOM is open source[1], and as GP alludes, is probably the most frequently ported game in existence, so its source code almost certainly appears multiple times in GPT-4's training set, likely alongside multiple annotated explanations.

[1] https://github.com/id-Software/DOOM

I'd define an arena as the pattern where the arena itself owns N objects. So you free the arena to free all objects.

My first job was at EA working on console games (PS2, GameCube, XBox, no OS or virtual memory on any of them), and while at the time I was too junior to touch the memory allocators themselves, we were definitely not malloc-ing and freeing all the time.

It was more like you load data for the level in one stage, which creates a ton of data structures, and then you enter a loop to draw every frame quickly. There were many global variables.

---

Wikipedia calls it a region, zone, arena, area, or memory context, and that seems about right:

https://en.wikipedia.org/wiki/Region-based_memory_management

It describes history from 1967 (before C was invented!) and has some good examples from Apache ("pools") and Postgres ("memory contexts").

I also just looked at these codebases:

https://github.com/mit-pdos/xv6-public (based on code from the 70's)

https://github.com/id-Software/DOOM (1997)

I looked at allocproc() in xv6, and gives you an object from a fixed global array. A lot of C code in the 80's and 90's was essentially "kernel code" in that it didn't have an OS underneath it. Embedded systems didn't run on full-fledges OSes.

DOOM tends to use a lot of what I would call "pools" -- arrays of objects of a fixed size, and that's basically what I remember from EA.

Though in g_game.c, there is definitely an arena of size 0x20000 called "demobuffer". It's used with a bump allocator.

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So I'd say

- malloc / free of individual objects was NEVER what C code looked like (aside from toy code in college)

- arena allocators were used, but global vars and pools are also very common.

- arenas are more or less wash for memory safety. they help you in some ways, but hurt you in others.

The reason C programmers don't malloc/free all the time is for speed, not memory safety. Arenas are still unsafe.

When you free an arena, you have no guarantee there's nothing that points to it anymore.

Also, something that shouldn't be underestimated is that arena allocators break tools like ASAN, which use the malloc() free() interface. This was underscored to me by writing a garbage collector -- the custom allocator "broke" ASAN, and that was actually a problem:

https://www.oilshell.org/blog/2023/01/garbage-collector.html

If you want memory safety in your C code, you should be using ASAN (dynamically instrumented allocators) and good test coverage. Arenas don't help -- they can actually hurt. An arena is a trivial idea -- the problem is more if that usage pattern actually matches your application, and apps evolve over time.

Doom