Cody Boone Ferguson
009e1b7522
The location of the link is in the About menu under the 'Contacting the IOCCC' and above 'Thanks for the help'. At first I had it at the very bottom, under 'IOCCC markdown guidelines', but it seemed better to have it closer to contacting the IOCCC. This is the same location in the no JavaScript menu (which, for those who do not know or forget, is not a requirement except for some screen sizes). The top level Makefile has a new 'security' rule. Updated make help. Typo fixes in make help. SECURITY.html has had a few updates as well: change the wording of entry code is unsupported (it now says 'ALL CODE IN ALL IOCCC ENTRIES IS UNSUPPORTED!!') and it now links to the mkiocccentry repo and how to report a possible security vulnerability in that repo; as that IS supported - and since there was reference to discussing security concerns is in SECURITY.html - even though the entries will not receive security updates - it seemed a good idea to have a link to report such security issues in the mkiocccentry repo. Perhaps the FAQ needs to be updated for this too.
To build:
make
To use:
make -B [MACHINE=your_machine.h] [TAPE=your_tape.h] [X=[0|1|2|3|4|5|6|7|8|9]] [V=[0|1|2]] run
Try:
./try.sh
Judges' remarks:
This is something we were fearing all along: that the C preprocessor is Turing-complete even without conditionals and recursive file inclusion as some kind of a rewriting system. Now we have the proof!
Author's remarks:
Preprocessor Turing Engine
Features
- Turing machine runs in preprocessor
- universal (unlimited configurable states, symbols, and tape)
- no
#ifs or other conditional directives, only#defines - no recursive
#include - single compiler run (no repeated preprocessing)
- no variadic macros
- verbosity levels:
V=0(default) only prints the final tapeV=1additionally prints one tilde character per machine step (slow)V=2additionally prints details on each machine step (slow; generates large files)
- make target
runruns./progand filters a little statistics out of the verbose output X(defaults to 3) sets the maximum number of steps: M(X) ~ 8X
Limitations
If the machine does not halt after M(X) steps, you will see unexpanded
macros in the output.
Compiler warnings
If V=1 or V=2 is used, you may see "warning: string length is greater than the length '4095' ISO C99 compilers are required to support".
Programming
Implementing your own Turing machine is easy. Take a look at the supplied header files for examples.
Tape Symbols
Every symbol used (except _) must be explicitly declared using
#define sym_SYMBOL(sym, _SYMBOL) sym
Example:
#define sym_1(sym, _1) sym
Tape
The initial content of the tape must be defined in the tape header using a triple like:
#define tape ((((,),...l2), l1), c, (r1, (r2..., (,))))
l1,l2, ... are the symbols to the leftcis the symbol at the current positionr1,r2, ... are the symbols to the right
The empty pairs (,) represent the continuations of the tape, filled with
underscore symbols (_). They are expanded on demand.
State Machine
All transitions are defined in the machine header using the syntax
#define CURRENT_SCANNED (WRITE, MOVEMENT, NEXT)
where
CURRENTis the current state.SCANNEDis the symbol at the current position.- The whitespace before the parentheses is significant.
WRITEis the symbol to be written to the tape.MOVEMENTisLfor left,Rfor right; don't specify anything if you want no movement.NEXTis the next state.
There must be a state A defined, which becomes the initial state of the
machine.
To halt the machine, use the keyword break as in
#define A_1 (2, break)