Cody Boone Ferguson
3f59415c9d
Make lines beginning (in markdown files) 'BTW' bold. Rebuilt the respective html pages. Slight update to abstract in two entries (1985/shapiro and 1994/shapiro). One is changing 'defines' to '#defines' and the other was a typo fix. Fixed make gen_next: added missing new files. Various fixes in next/register.html (typos and other things).
277 lines
10 KiB
Markdown
277 lines
10 KiB
Markdown
## To build:
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``` <!---sh-->
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make
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```
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There is an alternate version based on the author's remarks. See [Alternate
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code](#alternate-code) below for more details.
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### Bugs and (Mis)features:
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The current status of this entry is:
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> **STATUS: INABIAF - please DO NOT fix**
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For more detailed information see [2001/dgbeards in bugs.html](../../bugs.html#2001_dgbeards).
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## To use:
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``` <!---sh-->
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./dgbeards
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```
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## Alternate code:
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The author provided a way to speed it up a bit and also how to make it so it
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doesn't crash on losing. The idea that it crashes on losing was too good to
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lose but this alternate version has the former change. If you wish to remove
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this you can look at the author's remarks and make the change.
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### Alternate build:
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``` <!---sh-->
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make alt
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```
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### Alternate use:
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``` <!---sh-->
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./dgbeards.alt
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```
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## Try:
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See if you can figure out how to make the computer always lose ('win' :-) ).
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It's a very simple thing to do. Read the author's remarks for clues.
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This game crashes if it loses.
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## Judges' remarks:
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This is probably the worst AI we've ever seen. So, then, why did
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the entry win? Because it's *trying* to lose.
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This is also one of the first chess games we've seen.
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Of particular interest is the author's decision that the program should
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crash if it loses. I've played chess with a lot of people like that, and
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I appreciate the realism.
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**BTW**: if your goal is to lose and you do does that mean you win? :-) What does
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winning mean in a game you're supposed to lose at?
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## Author's remarks:
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### FAQ
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#### Q: What does this program do?
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A: It lets the user play two player or single player games of [suicide
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chess](https://en.wikipedia.org/wiki/Losing_chess). Suicide Chess (also known as
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Losing Chess) is a variant of normal chess. It is played on the same board and
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uses the same pieces. Here is a list of the differences:
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1. The object of the game is to get to a position where you have no legal
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moves. This is usually accomplished by losing all of your pieces.
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Sometimes, the game can end when you still have some pawns on the board,
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but they are blocked and cannot move. The general rule is if a player
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has no legal moves, the game is over. The entry is the player with fewer
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pieces on the board. This is almost always the same player that had no
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moves, but not always.
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2. In suicide chess, piece captures are compulsory. If a player can
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capture an opponent's piece, he is required to do so. If he can capture
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more than one of the opponent's pieces or can capture one piece with more
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than one of his own pieces, he can choose which capture to play.
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3. The king is not significant. There is no concept of check and the king
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can be captured.
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4. Because of rule 3, pawns are allowed to promote to a king.
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5. Castling is not allowed.
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#### Q: How do you use this program?
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A: The program is fairly straightforward. When you start the program,
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it displays the opening position for a game of suicide chess and waits
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for user input. Commands are as follows:
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- `quit` quits the program
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- `g` causes the computer to make a move
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Moves are represented by the long algebraic notation for the move. For those
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not familiar with long algebraic notation, a move consists of a square to move
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from followed by a square to move to. Squares are denoted by a letter and a
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number. The letter specifies the column or file of the square and the number
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specifies the row rank. Files are named from left to right by the letters `A` -
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`H`. Rows are numbered from bottom to top with the numbers `1` - `8`. A sample
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move from the opening position is `E2E3`. This means to move a piece from
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square `E2` to `E3`. From the opening position, this corresponds to moving the
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king pawn forward one square. This is generally to be considered one of the
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best opening moves in suicide chess. All moves, captures and otherwise, are
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represented with this notation. A special case is pawn promotion moves. They
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use the same notation followed by an `=` and a letter representing the piece to
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promote to. The letters are `R`, `N` , `B`, `Q`, `K` representing rook, knight,
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bishop, queen, and king respectively. The letters must be upper case.
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You can also specify a command line argument of a single digit to change
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the search depth of the program. If no argument is specified, it
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defaults to a depth of 3.
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#### Q: Are there any limitations in your program?
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A: Yes. The first of the limitations is that you can only play legal
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moves according to the rules of suicide chess. En passant captures are
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not recognized. They are rarely encountered in suicide chess and when
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they do happen, they usually do not change the outcome of the game. As
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mentioned above, castling is not allowed either.
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It also does not detect the end of the game. It can see sure wins or
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losses several moves ahead, but does not announce the end of a game nor
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the winner. Given the existing code it is easy to do this, but it was
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deemed unnecessary fluff.
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#### Q: What is the playing strength of this program?
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A: Playing strength is a relative term. Relative to other computer
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programs that play suicide chess, it is about the bottom. There is one
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freeware program in existence called `kenny` that this program can beat,
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but that is about it.
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Suicide chess is a very tactical game. Most humans who do not have any
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experience in suicide chess will lose to this program. The [Free Internet
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Chess Server](http://www.freechess.org) is a free online chess server
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that supports suicide chess. This server keeps track of ratings. The
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human ratings for suicide chess range from 1000 to about 2400. This
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program would probably be rated somewhere around 1700-1900. It is better
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than most players, but will get destroyed by experienced human opponents.
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This program searches to a fixed depth of 3
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[ply](https://en.wikipedia.org/wiki/Ply_(game_theory)). Because it does not
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search very deep, it performs very poorly in quiet strategic positions.
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In such positions, it will often just shuffle pieces around aimlessly
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until a tactical exchange presents itself.
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A small amount of randomness has been added to make the program a more
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interesting opponent. To avoid a call to `srand(3)`, `rand(3)` and the
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extra code for the required include files, the `time(3)` function is used as
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the source of random data. It is a slow function, and since it is
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executed inside the search loop, there is a significant performance
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decrease. To make it faster, replace the `time(3)` call with `rand(3)` and add
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the line `srand(time(0));` to the beginning of `main()`. I used the more
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inefficient `time(3)` function to illustrate a different (and somewhat
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obfuscated?) way of generating random numbers.
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#### Q: Why is this program obfuscated?
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A: Here are several reasons:
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First, without preprocessing, the code is not easy to read. The
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preprocessor is used to compress the code and obfuscate it. The main
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obstacle to entering this program is the source code size limit. This is
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the reason that the preprocessor was used so liberally. It is one of the
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best ways to compress C source code.
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Second, when possible, variables in the program were made global. Their
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names are not descriptive and they are used for a variety of purposes
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throughout the program. Because of this, it is difficult to determine
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exactly what the code does even after preprocessing and beautifying the
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code.
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Third, all function names are a single character and are obviously not
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descriptive of they're actual purpose. Again this serves the dual
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purpose of compression and obfuscation.
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Fourth, most string variables have been encoded. This encoding serves
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to obfuscate the program as well as reduce the number of countable
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characters and get the program under the size limit of this year's IOCCC.
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There are some places where other simple encoding methods are used to
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hide the real purpose of strings. These layers of obscurity cannot be
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penetrated by just preprocessing and beautifying the program.
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Fifth, various small obfuscations have been used in places all over the
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program. Short circuit evaluation is used as a substitute for `if()`
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statements in some places. The ternary operator is used. In the
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author's opinion, use of the ternary operator is almost always a strong
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argument for employee turnover.
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Last, if you have succeeded in wading through the previous layers of
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obfuscation, you are confronted by the fact that the game that it
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implements is an obscure game. Casual inspection of the program might
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lead one to believe that it is an implementation of classic chess, but
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this is not so.
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#### Q: What about the compiler warnings?
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A: When compiled with `gcc -Wall`, the compiler generated the following
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warnings:
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> suggest parentheses around `+` or `-` in operand of `&`<br>
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> array subscript has type '`char`'<br>
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> return type defaults to '`int`'<br>
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> control reaches end of non-void function<br>
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> value computed is not used
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The `value computed is not used` warning happens because I use the `&&`
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operator and take advantage of short circuit evaluation instead of using
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an `if()` statement.
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The `suggest parentheses...` warnings are given because of expressions
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that depend on operator precedence details in the C language.
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Eliminating these warnings would reduce obfuscation.
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The other warnings are there because it would require more code to
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eliminate them and that can't be done given the size limit.
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#### Q: Why does this program crash when it loses?
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A: What better way to admit defeat? The author thought this was
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appropriate sportsmanship for a program of this genre and can think of
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no worse job than trying to find an elusive bug in an intentionally
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obfuscated program.
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[**Judges' note**: This was followed by a description of the bug, and
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the comment:]
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Note, if this program wins, the author thinks it would be good to leave
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this information out of the remarks and encourage others to try and
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figure it out for themselves.
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[Should you be too lazy (or time-efficient or affected by 'real life' :-) ) to
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figure it out yourself, here's the author's fix.]
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This bug can be fixed in a number of ways, but there is a way that adds only one
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byte to the source code. In the statement `s=(e=-V(n-1,o))>s?Y=G,e:s;` change
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the `>` to a `>=` and the bug will be gone.
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<!--
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Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.
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You are free to share and adapt this file under the terms of this license:
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Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
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For more information, see:
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https://creativecommons.org/licenses/by-sa/4.0/
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-->
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