The 29th International Obfuscated C Code Contest (IOCCC) 2025 Winners
Posted by matt_d 3 days ago
Comments
Comment by haunter 3 days ago
https://github.com/ioccc-src/winner/blob/master/2025/ncw1/pr...
The author, Nick Craig-Wood, is the creator of rclone!
Comment by nickcw 2 days ago
If you want to see how the sausage was made, here is the source:
https://github.com/ncw/ioccc-gameboy
You'll find an unobfuscated version (kind-of) there too. This the the one I actually worked on then I had a program squash all the variable names and squeeze it into the gameboy shape
The size limit for the entry was the killer. You are allowed 2503 non white space characters (a simplification - the rules are complicated) in IOCCC entries and 4K total code size. This isn't a lot to fit a Z80 processor and a GameBoy hardware emulator in!
I first wrote a full Gameboy emulator in C. It started out at about 6000 non white space characters. I then spent about about 100 hours work trying to get it to fit into the 2503 limit. For a long time I wasn't sure it was going to fit.
I decided making the emulator play Tetris (which is a fairly simple game) was the target so I stripped out features like the half carry flag in the Z80 emulator and the windowing system in the Gameboy emulation which Tetris didn't need. I also abused the C code terribly doing things with implicit int I can never un-see. I also got creative with the IOCCC rules which are implemented in a C program which checks your source and I spent some time reverse engineering that looking for loopholes! I discovered that the operators defined in <iso646.h> only count for one token which was very useful.
Once I had it small enough I had to supply some games to run with it. I created 4, a test program written in z80 assembler, a pi calculator (written in assembler), a 3d tic tac toe game (written in C with gbdk-2020) and a chess program also written in C. I discovered that quite a few open source games ran on the emulator too so I added a downloader for those where I could. Apparently not many games use BCD arithmetic - who would have thought!
It was a fun project.
Comment by binji 2 days ago
Comment by kees99 2 days ago
GCC says there are a bunch of undefined symbols, first one being "R" right in the beginning:
typedef unsigned char u;
u w,X,T,D[1<<16],t[]=R,U=255;Comment by dezgeg 2 days ago
Comment by nickcw 2 days ago
Comment by toast0 2 days ago
Comment by ncr100 2 days ago
Comment by taneq 1 day ago
Comment by sourcecodeplz 3 days ago
Comment by 1vuio0pswjnm7 2 days ago
Comment by trumpdong 2 days ago
Comment by qingcharles 2 days ago
Comment by Waterluvian 2 days ago
Comment by s-macke 2 days ago
[0] https://github.com/ioccc-src/winner/blob/master/2025/cable/p...
[1] https://github.com/ioccc-src/winner/blob/master/2025/cable/R...
Comment by cpldcpu 2 days ago
>This VM implements an OISC - a One Instruction Set Computer. That instruction takes three signed 32-bit operands, a, b and c, and runs a program from memory m[] as follows:
1 PC (program counter) starts at 0
2 Fetch the next instruction (32-bit signed operands a, b and c)
3 If the low bit on any operand is set, remove it, and replace that operand with m[operand] i.e., a dereference of that address
4 Set m[b] = m[b] - m[a]
5 If m[b] is 0 or negative, set the PC to c, otherwise increment PC by 3 words
6 Go to step 2
Comment by jpegqs 1 day ago
This dereference option makes a second instruction, this is not OISC.
Comment by stevekemp 2 days ago
I could have gone all out writing standard library routines for opening files, running shell commands, coding strstr, strcpy, and similar. And to be honest I did implement some things I didn't need as part of the learning process (for example print(getenv("HOME")) works). But I soon realized I needed some example programs to test things and show off.
So of course the first real program I implemented was a brainfuck interpreter. Which means my language is now, indirectly, turing complete!
My early versions took 9 minutes to output the famous mandelbrot program, so I had to make a bunch of optimizations, and later implemented support for switch/case statements to speed things up. Now I can generate the same output in two minutes - so room for improvement, but also a good bit of progress!
Cheating by implementing another language in my own was very very satisfying. Though of course this is all for fun/learning and not intended to be used seriously by anybody, not even myself!
Comment by gsliepen 1 day ago
Comment by ralferoo 2 days ago
There's the one here: Set m[b] = m[b] - m[a]
Then it links to the reference implementation on github [2] which says you just need the napkin notes [3], which is dividing everything read by 4, which is corroborated by the reference implmentation [4], but it's not clear why 4 is chosen here rather than 2, as it seems to waste a bit. Was this bit needed, or is it reserved for future expansion?
I presume the original implementation didn't do the divide by 4 and it was added later, but I don't see why it was needed, other than perhaps just making LLVM code gen a little easier. I'd need to work through lots of examples to work out if the system as described is impossible without dividing by 4 (although you'd presumably only be able to access even addresses, and the PC increases by 3 each time, so it would definitely be annoying to refer to code locations).
Then the reference implementation starts doing magic when location 64 is accessed, overwriting locations 64-67 with the current time, which is mentioned in the napkin description, but not the description on the main page.
Both descriptions mention the magic -1 address, so it seems strange that the very implementation-dependent UTC clock isn't also implemented with -ve addresses rather than trashing memory that is otherwise free for the implementation to use as desired.
Both descriptions also mention the regular timer interrupt process, which also seems disappointing, reusing address 0 as the interrupt handler location and 1 as the saved PC, which means that you have to overwrite the initial entry point at location 0 as soon as the program starts.
[1] https://eternal-software.org/
[2] https://github.com/adriancable/eternal
[3] https://github.com/adriancable/eternal/blob/main/docs/napkin...
[4] https://github.com/adriancable/eternal/blob/main/vm/vm.c
Comment by ralferoo 2 days ago
Comment by s-macke 2 days ago
https://www.youtube.com/live/MoWCwZx1Swc?si=eIOlRsKWNKRVRZeB...
Comment by plasticeagle 2 days ago
Comment by s-macke 2 days ago
Comment by yayitswei 2 days ago
"The IOCCC has a rich history of remarkable winning entries created by authors who skillfully employed various techniques (often their own tools) to develop their code."
Comment by tgv 2 days ago
Also, the reverse is interesting: how well can they guess the function of the obfuscated code?
Comment by Catloafdev 2 days ago
Comment by Chu4eeno 1 day ago
All the big labs have plenty of proprietary (i. e. paying PhD holders good money for writing stuff) and synthetic training data now compensating for the lack of "naturally occuring" SUBLEQ and similar stuff.
Comment by omoikane 2 days ago
I think it's great that IOCCC accepts code that might have been built with machine assistance, because it makes the purely handcrafted winners seem even more valuable.
Comment by zerr 2 days ago
Comment by asfjhq 2 days ago
https://www.ioccc.org/2025/rules.html
It seems to refer to custom code generators. Why would they mean AI if they explicitly talk about a "rich history" (when AI wasn't available)?
Comment by GTP 2 days ago
The long tradition refers to the use of tooling in general, and could mean that, since past tools were accepted, recent tools like LLMs can be fair game as well.
But, since there can be doubts about this interpretation, them saying explicitly if LLMs are permitted or not could be beneficial. But then again, maybe they don't want to commit to an hard rule and have more freedom to decide on a case by case basis, or just don't advertise that LLMs are welcome to prevent a flood of vibe-coded submissions.
Comment by rtk_asp 2 days ago
In both cases you cannot get permission.
Comment by tonyarkles 2 days ago
On the “stolen” side, so far the courts have not generally agreed with that perspective except in cases where there is actually an existing copyrighted work that the LLM output is substantially similar to.
On the not-copyrightable side, the direct output of an LLM is generally legally seen as not copyrightable, but significant human modification or editing/reworking/steering/compilation (as in compiling a bunch of LLM-generated fragments into a functional whole) is still likely to be copyrightable.
Comment by GTP 2 days ago
Comment by ollybee 2 days ago
Comment by ASalazarMX 1 day ago
Comment by aquir 3 days ago
Comment by lifebeyondfife 2 days ago
Comment by crazygringo 2 days ago
When most visitors obviously just want to glance at the programs and see what they do, this is horrifically organized.
Comment by layer8 2 days ago
Comment by hugh-avherald 2 days ago
Comment by drfloyd51 2 days ago
Comment by TuringTourist 2 days ago
Comment by roer 2 days ago
One of the main characters is called Fern, and she almost exclusively uses the common offensive magic of Zoltraak.
Comment by omoikane 2 days ago
Comment by normanthreep 2 days ago
Comment by roer 2 days ago
Comment by normanthreep 2 days ago
Comment by perching_aix 2 days ago
Comment by msk-lywenn 2 days ago
Comment by nickcw 2 days ago
Comment by bbbbbr 2 days ago
Great project btw
Comment by locao 2 days ago
– And?
– I'm sorry I wasted your time. I just can't understand it.
They burst into laughs and asked me to start the joining process.
I wonder if people still make fun of interns. I still have a good laugh when I remember myself freaking out.
Comment by EGreg 2 days ago
So Obfuscated C Code Contest works but Capture the Flag doesn't? Because of AI?
https://twit.tv/posts/tech/ai-disrupts-capture-flag-what-mea...
Comment by omoikane 2 days ago
Maybe you are asking "can't someone think up a clever idea and ask the AI to implement it according to IOCCC constraints?" And I believe current AI tools are still unable do that at a level that the human judges find worthy.
Comment by TZubiri 2 days ago
Comment by purpleidea 1 day ago
Comment by ticulatedspline 1 day ago
Based on that it Looks like the contest starts late and runs into the next year. the 2025 rules were finalized in December.
Comment by LearnYouALisp 2 days ago
Comment by stiray 2 days ago
All my love <3 <3 <3 to organizers, thank you for continuing the IOCCC context, please never go away again!
Comment by Gathering6678 2 days ago
Comment by sathyayoshi 2 days ago
Comment by tomcloney007 2 days ago
Comment by swordlucky666 2 days ago
Comment by nsoonhui 2 days ago
Do I miss anything?
Comment by s-macke 2 days ago
They also lack the creativity needed for those entries. Obfuscation is only one part of it. Coming up with the idea is another. Many entries also have special qualities that make them true works of art.
Comment by awesome_dude 2 days ago
Comment by esikich 2 days ago
Comment by fooker 2 days ago
Have you tried it or are you guessing this?
Comment by s-macke 2 days ago
For example:
if (x == 1 || x == 2) { ...
can be transformed into: if (!(2+x*x-3*x)) { ...
An LLM will do this if you explicitly ask it to, but not on its own.[0] https://github.com/ioccc-src/winner/blob/master/2024/macke/p...
Comment by tromp 2 days ago
if (!(x/2-1)) { ...
EDIT: Oops, confused the original with x==2 || x==3. Instead, we can use !(x-1>>1), which precedence rules parse as !((x-1)>>1).Comment by extrano84 2 days ago
this statement is equivalent to x==2 | x==3.
For example, x=3, 3/2 = 1 then 1-1 = 0 so that !(0) is 1 or true. Also for x=1, 1/2 = 0 then 0-1 = -1 and !(-1) = 0 or false.
I agree with your point in general though about size constraints.
Comment by alienbaby 2 days ago
Comment by Mankaninen 2 days ago
Comment by fooker 2 days ago
if(x-1<2&&x)...
if((1<<x)&6)...
if(x<3&x)...
if(3%x&&x<3)...
if(!((x-1)*(x-2)))
if(!(x^1|x^2))...
if(!(x*x-3*x+2))Comment by listeria 2 days ago
(2) fails for (x % 32 in [1, 2]) due to UB
(3) fails for x == 2
(4) crashes for x == 0
(5) is the same polynomial, only factorized
(6) always returns 0
(7) is the same polynomail reordered
But this works for any value of x:
x<2==2-x
or for something shorter: x<3&x>0
but that's not bery obfuscatedComment by nsoonhui 2 days ago
Are you sure they still can't do it?
Comment by lifthrasiir 2 days ago
Comment by GuB-42 2 days ago
If anything, it is closer to code golf, the main obfuscation is often a result of all the trickery needed to do something impressive in a small amount of code. Of course, minification techniques are used, like renaming variables to single character and messing with the formatting, but that's the boring part, no one is going to win because of that.
Another aspect is being clever and unique, and abusing the rules is often rewarded... once. LLMs are not good at that. The judges are human, the code needs to a appeal to a human, not just be hard to understand.
Comment by jjav 2 days ago
That human art is worth the humanity in the art.
As soon as anything is automated, it's worth nothing.
Comment by zabzonk 2 days ago
Comment by GTP 2 days ago
Comment by visha1v 2 days ago
Comment by layer8 2 days ago
Comment by tjpnz 2 days ago
Comment by hulitu 2 days ago
School ? /s
Comment by larodi 3 days ago
Comment by shakna 2 days ago
> You are free to use whatever tools you wish to write your code. This includes tools that are AI based, LLM (large language model), Virtual coding assistants, code generators, or similar tools, as well as your own tools. The IOCCC judges do not discriminate on the basis of the tools used to write obfuscated C code so long as you are the ultimate author of the code you submit.
Comment by lifthrasiir 2 days ago
Comment by nickcw 2 days ago
Claude seems OK with it now, so I don't know whether that was a glitch but it was quite funny.
Comment by adampunk 2 days ago
Comment by larodi 2 days ago
/curious though given the very nice conversation we're having here, why the parent topic gets down-voted. is neither off-topic, nor rude.../
Comment by lifthrasiir 2 days ago
Comment by TZubiri 2 days ago
Comment by lifthrasiir 2 days ago
Comment by AlotOfReading 2 days ago
Comment by t_mahmood 2 days ago
Comment by rurban 2 days ago
Comment by lifthrasiir 2 days ago
- The number of winning entries and losing entries that get revealed later in public suggests that this number should be at least 50.
- The number of judging rounds, as the FAQ says, is at least 3 and possibly more. If each judging round eliminates about a half of entries, we should expect at least 10 submissions per each winning entries. I personally think the actual elimination rate can be as low as 1--20% at the end, but at least first few rounds should be easy so I think this is a good minimum guess: 1--200.
- The current number of individual judges is just enough for the three-digit number of submissions. It has a striking resemblance with typical academic conferences with typical acceptance rate, by the way! If there were thousands of submissions (like today's AI conferences...) there ought to be much more judges, and more importantly, more levels of judges so that each judge can do just enough work throughout the entire process. So this establishes the maximum guess: 1,000.
- My best guess is simply a geometric mean of two extrema.