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The 29th International Obfuscated C Code Contest (IOCCC) 2025 Winners (https://www.ioccc.org)

333 points by matt_d about 14 hours ago | 77 comments | View on ycombinator

haunter about 14 hours ago |

The GameBoy emulator's code also looks like the GameBoy. Slow clap this is insane, definitely my favorite entry.

https://github.com/ioccc-src/winner/blob/master/2025/ncw1/pr...

The author, Nick Craig-Wood, is the creator of rclone!

s-macke about 12 hours ago |

My favorite is the 366-byte C program emulator that can run Linux and Doom [0]. The VM implements an OISC - a One Instruction Set Computer [1].

[0] https://github.com/ioccc-src/winner/blob/master/2025/cable/p...

[1] https://github.com/ioccc-src/winner/blob/master/2025/cable/R...

yayitswei about 13 hours ago |

In case anyone was wondering, the IOCCC specifically permits LLM use in their guidelines.

"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."

aquir about 14 hours ago |

The website itself is obfuscated, it’s not easy to find the C sources at all!

roer about 7 hours ago |

There's a Frieren [1] reference in there! https://www.ioccc.org/2025/yang2/index.html

One of the main characters is called Fern, and she almost exclusively uses the common offensive magic of Zoltraak.

[1] https://en.wikipedia.org/wiki/Frieren

ollybee about 11 hours ago |

I with the Underhanded C Contest would come back, it was far more interesting to me. No disrespect intended to the Obfuscated C competitors.

msk-lywenn about 7 hours ago |

OMG, my game boy game of life implementation is included in one of the winning entries!

stiray about 1 hour ago |

OOOOOH! IOCCC is back!

All my love <3 <3 <3 to organizers, thank you for continuing the IOCCC context, please never go away again!

locao about 5 hours ago |

Back in 2000 I was being interviewed for my first internship, to join a team of C programmers. They showed me one of the winner entries of the prior years, asked me to review the code and left the room. About 5 minutes later they came back:

– 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.

TZubiri about 11 hours ago |

I love the submissions of IOCCC generally, but the schedule and submission process looks like a mess, is that part of the joke? Or is it just because being consistent and designing a simple process is hard¡

Gathering6678 about 6 hours ago |

There's another contest called Underhanded C that I enjoyed a lot reading, but it has been inactive for a decade at this point...

tomcloney007 about 4 hours ago |

[flagged]

swordlucky666 about 6 hours ago |

[dead]

nsoonhui about 12 hours ago |

I'm not sure this kind of competition is still meaningful, given that LLM can easily convert a program clearly written in any programming language to the most obfuscated C code, and can still easily verify it's correctness in an automated way.

Do I miss anything?

larodi about 13 hours ago |

Tis a pity to not have LLMs compete, given level of obfuscation they be capable of.

rurban about 13 hours ago |

So like at a film festival, 90% of the entries won a price, but unlike a film festival there's not a single best. Weird, like modern education.