[2020], and written for IOCCC: The International Obfuscated C Code Contest.
This was awarded "Best of Show - abuse of libc" at the time[0]. See also the judges' remarks[1]:
This program consists of a single printf(3) statement wrapped in a while loop. You would not think that this would amount to much, but you would be very, very wrong. A clue to what is happening and how this works is encoded in the ASCII art of the program source.
How did we end up with printf - within a loop - being Turing-complete? Was it designed that way from the beginning? Were new features added over time until we got there?
Having something Turing-complete is surprisingly easy, and it hides everywhere. The repository have a small document that explains how you can use printf() as a computer : it can performs additions, logical union and negation, which is enough.
It was unintentional, but Ken Thompson being Ken Thompson, can't be 100% sure.
It was probably unintentional, yeah, I don't recall any mentions of early printf being overloaded to do stuff, nor is it clear why you would do that since you're using it in a much more convenient Turing-complete language already (C).
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This was awarded "Best of Show - abuse of libc" at the time[0]. See also the judges' remarks[1]:
This program consists of a single printf(3) statement wrapped in a while loop. You would not think that this would amount to much, but you would be very, very wrong. A clue to what is happening and how this works is encoded in the ASCII art of the program source.
[0] https://www.ioccc.org/2020/index.html
[1] https://www.ioccc.org/2020/carlini/index.html
Alex: "Its primary purpose is to serve as The One True Debugger."
(It has certainly served me well.)
Deleted Comment
It was unintentional, but Ken Thompson being Ken Thompson, can't be 100% sure.
It was probably unintentional, yeah, I don't recall any mentions of early printf being overloaded to do stuff, nor is it clear why you would do that since you're using it in a much more convenient Turing-complete language already (C).