Author:

• Name: Doug Beardsley
  Location: US - United States of America (United States)

To build:

    make

There is an alternate version based on the author’s remarks. See Alternate code below for more details.

Bugs and (Mis)features:

The current status of this entry is:

STATUS: INABIAF - please DO NOT fix

For more detailed information see 2001/dgbeards in bugs.html.

To use:

    ./dgbeards

Alternate code:

The author provided a way to speed it up a bit and also how to make it so it doesn’t crash on losing. The idea that it crashes on losing was too good to lose but this alternate version has the former change. If you wish to remove this you can look at the author’s remarks and make the change.

Alternate build:

    make alt

Alternate use:

    ./dgbeards.alt

Try:

See if you can figure out how to make the computer always lose (‘win’ :-) ). It’s a very simple thing to do. Read the author’s remarks for clues.

This game crashes if it loses.

Judges’ remarks:

This is probably the worst AI we’ve ever seen. So, then, why did the entry win? Because it’s trying to lose.

This is also one of the first chess games we’ve seen.

Of particular interest is the author’s decision that the program should crash if it loses. I’ve played chess with a lot of people like that, and I appreciate the realism.

BTW: if your goal is to lose and you do does that mean you win? :-) What does winning mean in a game you’re supposed to lose at?

Author’s remarks:

FAQ

Q: What does this program do?

A: It lets the user play two player or single player games of suicide chess. Suicide Chess (also known as Losing Chess) is a variant of normal chess. It is played on the same board and uses the same pieces. Here is a list of the differences:

1. The object of the game is to get to a position where you have no legal moves. This is usually accomplished by losing all of your pieces. Sometimes, the game can end when you still have some pawns on the board, but they are blocked and cannot move. The general rule is if a player has no legal moves, the game is over. The entry is the player with fewer pieces on the board. This is almost always the same player that had no moves, but not always.

2. In suicide chess, piece captures are compulsory. If a player can capture an opponent’s piece, he is required to do so. If he can capture more than one of the opponent’s pieces or can capture one piece with more than one of his own pieces, he can choose which capture to play.

3. The king is not significant. There is no concept of check and the king can be captured.

4. Because of rule 3, pawns are allowed to promote to a king.

5. Castling is not allowed.

Q: How do you use this program?

A: The program is fairly straightforward. When you start the program, it displays the opening position for a game of suicide chess and waits for user input. Commands are as follows:

• quit quits the program
• g causes the computer to make a move

Moves are represented by the long algebraic notation for the move. For those not familiar with long algebraic notation, a move consists of a square to move from followed by a square to move to. Squares are denoted by a letter and a number. The letter specifies the column or file of the square and the number specifies the row rank. Files are named from left to right by the letters A - H. Rows are numbered from bottom to top with the numbers 1 - 8. A sample move from the opening position is E2E3. This means to move a piece from square E2 to E3. From the opening position, this corresponds to moving the king pawn forward one square. This is generally to be considered one of the best opening moves in suicide chess. All moves, captures and otherwise, are represented with this notation. A special case is pawn promotion moves. They use the same notation followed by an = and a letter representing the piece to promote to. The letters are R, N , B, Q, K representing rook, knight, bishop, queen, and king respectively. The letters must be upper case.

You can also specify a command line argument of a single digit to change the search depth of the program. If no argument is specified, it defaults to a depth of 3.

Q: Are there any limitations in your program?

A: Yes. The first of the limitations is that you can only play legal moves according to the rules of suicide chess. En passant captures are not recognized. They are rarely encountered in suicide chess and when they do happen, they usually do not change the outcome of the game. As mentioned above, castling is not allowed either.

It also does not detect the end of the game. It can see sure wins or losses several moves ahead, but does not announce the end of a game nor the winner. Given the existing code it is easy to do this, but it was deemed unnecessary fluff.

Q: What is the playing strength of this program?

A: Playing strength is a relative term. Relative to other computer programs that play suicide chess, it is about the bottom. There is one freeware program in existence called kenny that this program can beat, but that is about it.

Suicide chess is a very tactical game. Most humans who do not have any experience in suicide chess will lose to this program. The Free Internet Chess Server is a free online chess server that supports suicide chess. This server keeps track of ratings. The human ratings for suicide chess range from 1000 to about 2400. This program would probably be rated somewhere around 1700-1900. It is better than most players, but will get destroyed by experienced human opponents.

This program searches to a fixed depth of 3 ply. Because it does not search very deep, it performs very poorly in quiet strategic positions. In such positions, it will often just shuffle pieces around aimlessly until a tactical exchange presents itself.

A small amount of randomness has been added to make the program a more interesting opponent. To avoid a call to srand(3), rand(3) and the extra code for the required include files, the time(3) function is used as the source of random data. It is a slow function, and since it is executed inside the search loop, there is a significant performance decrease. To make it faster, replace the time(3) call with rand(3) and add the line srand(time(0)); to the beginning of main(). I used the more inefficient time(3) function to illustrate a different (and somewhat obfuscated?) way of generating random numbers.

Q: Why is this program obfuscated?

A: Here are several reasons:

First, without preprocessing, the code is not easy to read. The preprocessor is used to compress the code and obfuscate it. The main obstacle to entering this program is the source code size limit. This is the reason that the preprocessor was used so liberally. It is one of the best ways to compress C source code.

Second, when possible, variables in the program were made global. Their names are not descriptive and they are used for a variety of purposes throughout the program. Because of this, it is difficult to determine exactly what the code does even after preprocessing and beautifying the code.

Third, all function names are a single character and are obviously not descriptive of they’re actual purpose. Again this serves the dual purpose of compression and obfuscation.

Fourth, most string variables have been encoded. This encoding serves to obfuscate the program as well as reduce the number of countable characters and get the program under the size limit of this year’s IOCCC. There are some places where other simple encoding methods are used to hide the real purpose of strings. These layers of obscurity cannot be penetrated by just preprocessing and beautifying the program.

Fifth, various small obfuscations have been used in places all over the program. Short circuit evaluation is used as a substitute for if() statements in some places. The ternary operator is used. In the author’s opinion, use of the ternary operator is almost always a strong argument for employee turnover.

Last, if you have succeeded in wading through the previous layers of obfuscation, you are confronted by the fact that the game that it implements is an obscure game. Casual inspection of the program might lead one to believe that it is an implementation of classic chess, but this is not so.

Q: What about the compiler warnings?

A: When compiled with gcc -Wall, the compiler generated the following warnings:

suggest parentheses around + or - in operand of &
array subscript has type ‘char’
return type defaults to ‘int’
control reaches end of non-void function
value computed is not used

The value computed is not used warning happens because I use the && operator and take advantage of short circuit evaluation instead of using an if() statement.

The suggest parentheses... warnings are given because of expressions that depend on operator precedence details in the C language. Eliminating these warnings would reduce obfuscation.

The other warnings are there because it would require more code to eliminate them and that can’t be done given the size limit.

Q: Why does this program crash when it loses?

A: What better way to admit defeat? The author thought this was appropriate sportsmanship for a program of this genre and can think of no worse job than trying to find an elusive bug in an intentionally obfuscated program.

[Judges’ note: This was followed by a description of the bug, and the comment:]

Note, if this program wins, the author thinks it would be good to leave this information out of the remarks and encourage others to try and figure it out for themselves.

[Should you be too lazy (or time-efficient or affected by ‘real life’ :-) ) to figure it out yourself, here’s the author’s fix.]

This bug can be fixed in a number of ways, but there is a way that adds only one byte to the source code. In the statement s=(e=-V(n-1,o))>s?Y=G,e:s; change the > to a >= and the bug will be gone.

Primary files

• dgbeards.c - entry source code
• Makefile - entry Makefile
• dgbeards.alt.c - alternate source code
• dgbeards.orig.c - original source code

Secondary files

• 2001_dgbeards.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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