Most Pointed Reaction

Judges' comments:

To use:

make
echo Some text | ./prog

Try:

echo IOCCC 2015 | ./prog | tee output.c
make output
./output

echo IOCCC 2015 | ./prog_c11 | tee output.c
make output
./output

echo IOCCC 2015 | ./prog_c++98 | tee output.c
make output
./output

Selected Judges Remarks:

Before analysing the code in detail we were able to guess two out of four tests this entry uses to tell the 5 languages/flavors apart. Can you find all four?

The way the text is encoded in the output doesn’t cease to amaze. Can you tell why an array of 512 elements is needed?

Author’s comments:

Fuuko is a sea star generator. Feed her some input through stdin to get lots of sea star patterns in stdout.

gcc -O3 -std=c90 fuuko.c -lm -o fuuko_c90
echo IOCCC | ./fuuko_c90 > output_c90.c

If you compile with a C99 compiler instead of C90, the sea stars will have eyes.

gcc -O3 -std=c99 fuuko.c -lm -o fuuko_c99
echo IOCCC | ./fuuko_c99 > output_c99.c

Don’t like sea stars? Use a C++98 compiler to get dango instead.

g++ -O3 -std=c++98 fuuko.c -lm -o fuuko_cpp98
echo IOCCC | ./fuuko_cpp98 > output_cpp98.c

Don’t like dango either? Use a C++11 compiler to get just circles (or swiss cheese, if you prefer that).

g++ -O3 -std=c++11 fuuko.c -lm -o fuuko_cpp11
echo IOCCC | ./fuuko_cpp11 > output_cpp11.c

Don’t like any of these patterns? Use a C11 compiler and there will be no extra patterns.

gcc -O3 -std=c11 fuuko.c -lm -o fuuko_c11
echo IOCCC | ./fuuko_c11 > output_c11.c

Regardless of which of these C/C++ dialects you choose, the output will all be valid C90 code that reproduces original input on stdout, filled with pointer dereferences (C stars).

Next time people ask you for a few pointers on C, you can run their question through Fuuko and give them pointers all day long.

Compatibility

Fuuko has been tested under these environments:

gcc 4.9.3 on Cygwin
gcc 4.9.2 on Linux
gcc 4.8.4 on Linux
gcc 4.6.3 on Linux (doesn’t support C11 nor C++11)
gcc 4.3.5 on JS/Linux
clang 3.5.2 on Cygwin (doesn’t work with optimization enabled, probably cygwin bug)
clang 3.5.0 on Linux
clang 3.4.1 on Linux
tcc 0.9.25 on JS/Linux (C99 only)

Features

The most obscure parts are in detecting the subtle differences in different dialects. The standard committees put a lot of effort into avoiding “quiet changes”, but Fuuko is still able exploit a few of those. It should be an interesting exercise for the reader to figure how she did it.

Output patterns are usually random (except for C11). The built-in random number generator is seeded using ASLR. On systems where ASLR is not so random (such as cygwin), you can introduce randomness by changing number of command line arguments to Fuuko.

Output is somewhat robust: corruption on most of the lines will usually result in a compiler warning. This is because the output is vastly redundant: For ~1K of input, expect output to be on the order of ~1MB, and take ~500MB of RAM to compile.

CRC32 of source code is embedded in the source code itself.

Process of writing this program is included in spoiler.html

Code layout is inspired by Ibuki Fuuko, for her love of sea stars.