Author:

• Name: Daniel Fischer
  Location: US - United States of America (United States)

To build:

    make all

To use:

    ./df

Try:

    ./try.sh

This will run the program in a loop until you exit (q when prompted or ctrl-c/intr).

Can you figure out a very simple pipeline to cheat?

Judges’ remarks;

Everyone talks about how data hiding can produce clearer code; I am pleased to offer this charming refutation.

The program is a simple game. A bit of observation reveals that the game has some data - but where? It’s unclear which of the contents of the program are used.

Curiously, the program only works if its source is in the directory it’s run in. More curiously, the program would fail if the program’s name’s second letter wasn’t r (the source has been changed for your convenience and this restriction no longer exist).

Modern design has come a long way since the unreadable, tightly-coupled systems we used to have.

Extra credit questions:

• Where are the words stored?
• How many words does this entry use?
• Can you add more words to the program and still make it work?
• Are there any misspelt words? If yes what are they?

Author’s remarks:

This program lets you guess English words. It displays an underscore for each letter in the word; guessing a letter that actually is in the word replaces the corresponding underscores with the letter itself. You can guess a letter simply by typing it in. If your C implementation requires it, you may have to hit Return before it is recognized. In this case, you can also type multiple guesses on the same line (completely solve it by entering abcdefghijklmnopqrstuvwxyz). Execution stops when all underscores have been replaced.

The program offers a number of different words to guess, time() is used to pick one at random. All words are eight characters long.

The source should compile with any ANSI C compiler (I used CodeWarrior w/ ANSI strict). Using non-ANSI compilers that implement the ANSI features it uses will not work (unless they defined __STDC__ 1 which they shouldn’t). Due to space restrictions, I did not use any trigraph sequences. It does not require any special -D defines.

The source passes lint without any complaint (if invoked with >/dev/null). (My lclint is unable to recover from some parts of it.)

Actually, the code not only is compliant with the ANSI specifications, but uses a near minimum subset of them. C keywords that were not used have been re(de)fined to avoid unnecessary introduction of new, unknown character patterns. The source also includes all ANSI headers it needs (after most of the functions have been used), and the declaration of main() follows the guidelines (but the return type has a different meaning and the arguments are either misused or unused). There also may be some compiler warnings. These are not bugs, but features. The more warnings, the better the compiler. There wouldn’t be any if I had been allowed to use some extra space for prototypes etc.

Multiple defines are used (but not all of them define), and #define y define is used with #y but the code doesn’t assume #y to expand to #define. I have also included comments in the code, and vital code in the comments. And of course there is code that doesn’t do anything but will crash the program if it is removed (just like those comments I mentioned above). Additionally, since you said you’d be preprocessing entries ignoring #includes I figured I should use some more of them instead of other obfuscation methods. Did I mention that preprocessed or beautified sources will crash or hang your system? The program will also crash on non-ASCII machines.

The executable needs its source file present in the current directory or, depending on your system, in your path. The name of the source file is not hard-coded, __FILE__ is used instead.

In the original version which was sent in to the contest, there were some restrictions on the file name:

• The second letter had to be a lowercase r.
• The third letter could never be a + or a b.

Valid names would have been pr4.c, pr.c, prog.c, brownie.c etc. My first private version would only run when compiled on a Friday. I decided it would be better this way… These restrictions have been removed for your convenience.

NOTICE to those who wish for a greater challenge:

If you want a greater challenge, don’t read any further: just try to understand the program via the source.

If you get stuck, come back and read below for additional hints and information.

How this entry works:

The following lines describe how this program works; if you don’t want to know it at this time, please skip them. If this entry would by some mistake win the contest, please do not rot13 this - I hate rot13 spoilers since it is somewhat complicated on a Mac to reverse them. Anyone out there should have enough discipline and rot13 shouldn’t be required, really. After all, we are not children anymore :-)

This paragraph is not part of the author’s remarks, but is a helpful gift from the judges; if you read too fast to stop yourself, this should give you enough time to stop, which you really need to do RIGHT NOW if you don’t want to read the obfuscation information: we mean it.

The source file needs to be present because the words are read from it. The wordlist is encoded within the source using a 24 entry sliding dictionary where lowercase letters are offsets into the dictionary, uppercase letters are new letters not yet in the dictionary, and all other characters are ignored. The words are spread over six lines in the source; decoding starts on a line after a tab and a whitespace have been found, and stops on a newline. The grin after the “Demonic Smiley” actually is one encoded letter while the string is completely ignored; and the cut in “cut here” is required while here is not.

“For extra credit”, explain why the words are sorted alphabetically (because I extracted them from a dictionary :-) )

The file name had to fulfill the restrictions mentioned above because __FILE__+1 was used as a second parameter to fopen(). (It essentially was fopen(__FILE__,__FILE__+1) ). This was an extra joke that doesn’t exist in the released version.

You probably discovered that the while(FILE) in main() is not a while loop but the statement that opens the file and initializes the dictionary. Similarly, int and signed have been redefined (to save space, of course).

The main function (the guessing part) is between the last #else..#endif, but still is declared before main(). The 5[O]() in main() calls this function. Similarly, most indexing operations have been changed to this form and I tried to write each such operation different.

Primary files

• df.c - entry source code
• Makefile - entry Makefile
• df.orig.c - original source code
• try.sh - script to try entry

Secondary files

• 1998_df.tar.bz2 - download entry tarball
• README.md - markdown source for this web page
• .entry.json - entry summary and manifest in JSON
• .gitignore - list of files that should not be committed under git
• .path - directory path from top level directory
• index.html - this web page

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