Author:

• Name: Oscar Toledo G.
  Location: MX - United Mexican States (Mexico)

To build:

    make

There are two alternate versions provided by the author. See Alternate code below.

To use:

    ./toledo [a ...]

Try:

    ./toledo a
    ./toledo a b

Alternate code:

Two alternate versions of this entry, toledo2.c and toledo3.c were provided by the author. Unfortunately, in 2024, it is not currently known what the differences are.

Alternate build:

To compile the alternate versions:

    make alt

Alternate use:

Use Use toledo2 and toledo3 as you would toledo above.

Judges’ remarks:

Challenge yourself with your ability to look 5, 6 or more moves ahead. Challenge your knowledge of C operator precedence. The following is the move analysis via recursion while it executes moves. All while playing by the rules of C and Chess within a single function!

Historical note:

When this entry was submitted the code was a recursive call to main() - that was it. In 2023 due to problems with clang, main() calls another function, pain(), which calls itself. But it might be said that the Chess is still a single function.

Author’s remarks:

What does this program

This is a chess program, it can work in two modes: two-players, and one player (always white) against the machine. To get the first mode, run the program without arguments:

    ./toledo

The other mode is accessible running the program with one argument (5-ply analysis):

    ./toledo a

Two arguments for 6-ply analysis:

    ./toledo a b

And each successive argument will analyze one ply more. There is no ply limit, but beyond 7 ply is very slow, try it at your own risk and computing time.

Entering movements

When it is your turn, you can enter your move, for example, as d2d4 and press the enter key. This will move the pawn at D2 to D4, assuming that a pawn is there (as it would be in the beginning). The computer will check move legality and will warn you of illegal moves. All legal chess moves are permitted.

One special case is when you are doing promotion, you must enter the move with an extra letter indicating the desired piece.

For example f7f8n (supposing you have a pawn on F7), will promote it to a knight; substitute n for the desired piece (N/Q/R/B).

Note that the program requires the piece letter; it will not select automatically a queen, so don’t be surprised if it doesn’t accept your move.

Game status

The computer will check for checkmate and stalemate. Also, after each machine move, it will show the score of the position: a higher number is better for the computer, i.e. worse for you.

Quirks

None.

Program operation

This is a good example of a chess program reduced to the essential. In order to get it into the contest limits, I used short but slow and unintelligible algorithms.

The interface accounts for only a fraction of the code, the core does multiples functions: it is called recursively to analyze and evaluate each ply, does alpha-beta pruning, move generation, machine playing, check detection, illegal move verification and does moves after they are verified.

It also sets a standard on ultra-mini-chess programs. The player and the computer can do all legal chess moves.

Additional features

Other features are:

• Illegal move verification.
• Checkmate detection.
• Stalemate detection.
• Computer is tough (check 7-ply and even in 5 ply can give a surprise to amateur players.

Obfuscation tricks

• Only one very modular C function.
• Extensive use of the ternary and comma operators; save a hard drive today.
• Extensive use of C operator precedence; all good C programmers remember it… I cannot.
• Exchanged operands every place possible. Someday someone will understand it.
• Mixed and multifunction expressions on statements, in good old-BASIC style.
• Macros used to hide C syntax: check unbalanced parenthesis and calls with empty arguments!
• Only includes strictly necessary standard headers, the linker takes care, and compiles faster… but I’m still not seeing the difference.
• Uses only one string, very easy to i18n ;)

Primary files

• toledo.c - entry source code
• Makefile - entry Makefile
• toledo.orig.c - original source code
• toledo2.c - alternate source code
• toledo3.c - second alternate source code

Secondary files

• 2005_toledo.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

---

Jump to: top